Communication system, base station device and communication terminal device

ABSTRACT

A signal is transmitted and received between a base station device and a communication terminal device that are included in a communication system, through a multi-element antenna including a plurality of antenna elements. At least one of the base station device and the communication terminal device includes a PHY processing unit that is a calibration unit that performs calibration of phases and amplitudes of beams formed by the antenna elements when the signal is transmitted and received. The PHY processing unit obtains a correction value for the phases and the amplitudes of the beams in the respective antenna elements so that the phases and the amplitudes of the beams are identical among the antenna elements, and performs the calibration based on the obtained correction value.

CROSS REFERENCE RO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. § 120 from U.S. application Ser. No. 16/751,467 filedJan. 24, 2020, which is a continuation of U.S. application Ser. No.16/417,752 filed May 21, 2019 (now U.S. Pat. No. 10,601,526 issued Mar.24, 2020), which is a continuation of U.S. application Ser. No.15/565,359 filed Oct. 9, 2017 (now U.S. Pat. No. 10,348,422 issued Jul.9, 2019), the entire contents of which is incorporated herein byreference. U.S. application Ser. No. 15/565,359 is a National Stage ofPCT/JP2016/061190 filed Apr. 6, 2016, which claims the benefit ofpriority under 35 U.S.C. § 119 from Japanese Application No. 2015-081060filed Apr. 10, 2015.

TECHNICAL FIELD

The present invention relates to a communication system in which radiocommunication is performed between a communication terminal device suchas a user equipment device and a base station device.

BACKGROUND ART

The 3rd generation partnership project (3GPP), the standard organizationregarding the mobile communication system, is studying communicationsystems referred to as long term evolution (LTE) regarding radiosections and system architecture evolution (SAE) regarding the overallsystem configuration including a core network and a radio accessnetwork, which will be hereinafter collectively referred to as a networkas well (for example, see Non-Patent Documents 1 to 13). Thiscommunication system is also referred to as 3.9 generation (3.9 G)system.

As the access scheme of the LTE, orthogonal frequency divisionmultiplexing (OFDM) is used in a downlink direction and single carrierfrequency division multiple access (SC-FDMA) is used in an uplinkdirection. Further, differently from the wideband code division multipleaccess (W-CDMA), circuit switching is not provided but a packetcommunication system is only provided in the LTE.

The decisions by 3GPP regarding the frame configuration in the LTEsystem described in Non-Patent Document 1 (Chapter 5) will be describedwith reference to FIG. 1. FIG. 1 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 1, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal per radio frame. The synchronizationsignals are classified into a primary synchronization signal (P-SS) anda secondary synchronization signal (S-SS).

Non-Patent Document 1 (Chapter 5) describes the decisions by 3GPPregarding the channel configuration in the LTE system. It is assumedthat the same channel configuration is used in a closed subscriber group(CSG) cell as that of a non-CSG cell.

A physical broadcast channel (PBCH) is a channel for downlinktransmission from a base station device (hereinafter may be simplyreferred to as a “base station”) to a communication terminal device(hereinafter may be simply referred to as a “communication terminal”)such as a user equipment device (hereinafter may be simply referred toas a “user equipment”). A BCH transport block is mapped to foursubframes within a 40 ms interval. There is no explicit signalingindicating 40 ms timing.

A physical control format indicator channel (PCFICH) is a channel fordownlink transmission from a base station to a communication terminal.The PCFICH notifies the number of orthogonal frequency divisionmultiplexing (OFDM) symbols used for PDCCHs from the base station to thecommunication terminal. The PCFICH is transmitted per subframe.

A physical downlink control channel (PDCCH) is a channel for downlinktransmission from a base station to a communication terminal. The PDCCHnotifies of the resource allocation information for downlink sharedchannel (DL-SCH) being one of the transport channels described below,resource allocation information for a paging channel (PCH) being one ofthe transport channels described below, and hybrid automatic repeatrequest (HARQ) information related to DL-SCH. The PDCCH carries anuplink scheduling grant. The PDCCH carries acknowledgement(Ack)/negative acknowledgement (Nack) that is a response signal touplink transmission. The PDCCH is referred to as an L1/L2 control signalas well.

A physical downlink shared channel (PDSCH) is a channel for downlinktransmission from a base station to a communication terminal. A downlinkshared channel (DL-SCH) that is a transport channel and a PCH that is atransport channel are mapped to the PDSCH.

A physical multicast channel (PMCH) is a channel for downlinktransmission from a base station to a communication terminal. Amulticast channel (MCH) that is a transport channel is mapped to thePMCH.

A physical uplink control channel (PUCCH) is a channel for uplinktransmission from a communication terminal to a base station. The PUCCHcarries Ack/Nack that is a response signal to downlink transmission. ThePUCCH carries a channel quality indicator (CQI) report. The CQI isquality information indicating the quality of received data or channelquality. In addition, the PUCCH carries a scheduling request (SR).

A physical uplink shared channel (PUSCH) is a channel for uplinktransmission from a communication terminal to a base station. An uplinkshared channel (UL-SCH) that is one of the transport channels is mappedto the PUSCH.

A physical hybrid ARQ indicator channel (PHICH) is a channel fordownlink transmission from a base station to a communication terminal.The PHICH carries Ack/Nack that is a response signal to uplinktransmission. A physical random access channel (PRACH) is a channel foruplink transmission from the communication terminal to the base station.The PRACH carries a random access preamble.

A downlink reference signal (RS) is a known symbol in the LTEcommunication system. The following five types of downlink referencesignals are defined: a cell-specific reference signal (CRS), an MB SFNreference signal, a data demodulation reference signal (DM-RS) being aUE-specific reference signal, a positioning reference signal (PRS), anda channel state information reference signal (CSI-RS). The physicallayer measurement objects of a communication terminal include referencesignal received power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)will be described. A broadcast channel (BCH) among the downlinktransport channels is broadcast to the entire coverage of a base station(cell). The BCH is mapped to the physical broadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH can be broadcast to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a communication terminal for enablingthe communication terminal to save power. The DL-SCH is mapped to thephysical downlink shared channel (PDSCH).

The paging channel (PCH) supports DRX of the communication terminal forenabling the communication terminal to save power. The PCH is requiredto be broadcast to the entire coverage of the base station (cell). ThePCH is mapped to physical resources such as the physical downlink sharedchannel (PDSCH) that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of multimediabroadcast multicast service (MBMS) services (MTCH and MCCH) inmulti-cell transmission. The MCH supports semi-static resourceallocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH) among the uplink transport channels. TheUL-SCH supports dynamic or semi-static resource allocation. The UL-SCHis mapped to the physical uplink shared channel (PUSCH).

A random access channel (RACH) is limited to control information. TheRACH involves a collision risk. The RACH is mapped to the physicalrandom access channel (PRACH).

The HARQ will be described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest (ARQ) and error correction (forward error correction). The HARQis advantageous in that error correction functions effectively byretransmission even for a channel whose communication quality changes.In particular, it is also possible to achieve further qualityimprovement in retransmission through combination of the receptionresults of the first transmission and the reception results of theretransmission.

An example of the retransmission method will be described. If thereceiver fails to successfully decode the received data, in other words,if a cyclic redundancy check (CRC) error occurs (CRC=NG), the receivertransmits “Nack” to the transmitter. The transmitter that has received“Nack” retransmits the data. If the receiver successfully decodes thereceived data, in other words, if a CRC error does not occur (CRC=OK),the receiver transmits “AcK” to the transmitter. The transmitter thathas received “Ack” transmits the next data.

The logical channels described in Non-Patent Document 1 (Chapter 6) willbe described. A broadcast control channel (BCCH) is a downlink channelfor broadcast system control information. The BCCH that is a logicalchannel is mapped to the broadcast channel (BCH) or downlink sharedchannel (DL-SCH) that is a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging information and system information change notifications. The PCCHis used when the network does not know the cell location of acommunication terminal. The PCCH that is a logical channel is mapped tothe paging channel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between communication terminals and a base station. The CCCHis used in the case where the communication terminals have no RRCconnection with the network. In the downlink direction, the CCCH ismapped to the downlink shared channel. (DL-SCH) that is a transportchannel. In the uplink direction, the CCCH is mapped to the uplinkshared channel (UL-SCH) that is a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to acommunication terminal. The MCCH is used only by a communicationterminal during reception of the MBMS. The MCCH is mapped to themulticast channel (MCH) that is a transport channel.

A dedicated control channel (DCCH) is a channel that transmits dedicatedcontrol information between a communication terminal and a network on apoint-to-point basis. The DCCH is used when the communication terminalhas an RRC connection. The DCCH is mapped to the uplink shared channel(UL-SCH) in uplink and mapped to the downlink shared channel (DL-SCH) indownlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicatedcommunication terminal. The DTCH exists in uplink as well as downlink.The DTCH is mapped to the uplink shared channel (UL-SCH) in uplink andmapped to the downlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a communication terminal. The MTCHis a channel used only by a communication terminal during reception ofthe MBMS. The MTCH is mapped to the multicast channel (MCH).

CGI represents a cell global identifier. ECGI represents an E-UTRAN cellglobal identifier. A closed subscriber group (CSG) cell is introduced inthe LTE, and the long term evolution advanced (LTE-A) and universalmobile telecommunication system (UMTS) described below.

The closed subscriber group (CSG) cell is a cell in which subscriberswho are allowed use are specified by an operator (hereinafter, alsoreferred to as a “cell for specific subscribers”). The specifiedsubscribers are allowed to access one or more cells of a public landmobile network (PLMN). One or more cells to which the specifiedsubscribers are allowed access are referred to as “CSG cell(s)”. Notethat access is limited in the PLMN.

The CSG cell is part of the PLMN that broadcasts a specific CSG identity(CSG ID) and broadcasts “TRUE” in a CSG indication. The authorizedmembers of the subscriber group who have registered in advance accessthe CSG cells using the CSG ID that is the access permissioninformation.

The CSG ID is broadcast by the CSG cell or cells. A plurality of CSG IDsexist in the LTE communication system. The CSG IDs are used bycommunication terminals (UEs) for making access from CSG-related memberseasier.

The locations of communication terminals are tracked based on an areacomposed of one or more cells. The locations are tracked for enablingtracking the locations of communication terminals and callingcommunication terminals, in other words, incoming calling tocommunication terminals even in an idle state. An area for trackinglocations of communication terminals is referred to as a tracking area.

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation, or commercial access service inUTRAN/E-UTRAN.

Non-Patent Document 2 discloses three different modes of the access tothe HeNB and HNB. Specifically, an open access mode, a closed accessmode, and a hybrid access mode are disclosed.

The individual modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a CSG cell where only CSG members are allowedaccess. In the hybrid access mode, the HeNB and HNB are operated as CSGcells where non-CSG members are allowed access at the same time. Inother words, a cell in the hybrid access mode (also referred to as ahybrid cell) is the cell that supports both of the open access mode andthe closed access m ode.

In 3GPP, among all physical cell identities (PCIs) is a range of PCIsreserved by the network for use by CSG cells (see Chapter 10.5.1.1 ofNon-Patent Document 1). Division of the PCI range is also referred to asPCI split. The information about PCI split (also referred to as PCIsplit information) is broadcast in the system information from a basestation to communication terminals being served thereby. Being served bya base station means taking the base station as a serving cell.

Non-Patent Document 3 discloses the basic operation of a communicationterminal using PCI split. The communication terminal that does not havethe PCI split information needs to perform cell search using all PCTs,for example, using all 504 codes. On the other hand, the communicationterminal that has the PCI split information is capable of performingcell search using the PCI split information.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Documents 4 and 5). TheLTE-A is based on the LTE radio communication system and is configuredby adding several new techniques to the system.

Carrier aggregation (CA) is studied for the LTE-A system, in which twoor more component carriers (CCs) are aggregated to support widertransmission bandwidths up to 100 MHz.

In the case where CA is configured, a UE has a single RRC connectionwith a network (NW). In RRC connection, one serving cell provides NASmobility information and security input. This cell is referred to as aprimary cell (PCell). In downlink, a carrier corresponding to PCell is adownlink primary component carrier (DL PCC). In uplink, a carriercorresponding to PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a serving cell group withPCell, in accordance with the UE capability. In downlink, a carriercorresponding to SCell is a downlink secondary component carrier (DLSCC). In uplink, a carrier corresponding to SCell is an uplink secondarycomponent carrier (UL SCC).

A serving cell group of one PCell and one or more SCells is configuredfor one UE.

The new techniques in the LTE-A include the technique of supportingwider bands (wider bandwidth extension) and the coordinated multiplepoint transmission and reception (CoMP) technique. The CoMP studied forLTE-A in 3GPP is described in Non-Patent Document 6.

The traffic flow of a mobile network is on the rise, and thecommunication rate is also increasing. It is expected that thecommunication rate and the traffic flow will be further increased whenthe operations of the LTE and the LTE-A are fully initiated.

Widespread use of smartphones and tablet terminals explosively increasestraffic in cellular radio communications, causing a fear of insufficientradio resources all over the world.

To deal with the problem of increased traffic, 3GPP is developingspecifications of Release 12. In the specifications of Release 12, theuse of small eNBs is studied to satisfy a tremendous volume of trafficin the future. In an example technique under study, a large number ofsmall eNBs are installed to configure a large number of small cells,thus increasing spectral efficiency for increased communicationcapacity.

In Release 12, dual connectivity is discussed as the technique ofconnecting a communication terminal to both a macro cell and a smallcell when the macro cell and the small cell overlap each other (seeNon-Patent Document 8).

For increasingly sophisticated mobile communications, the fifthgeneration (hereinafter also referred to as “5G”) radio access system isstudied, whose service is aimed to be launched in 2020 and afterward.For example, in the Europe, an organization named METIS summarizes therequirements for 5G (see Non-Patent Document 9).

Among the requirements in the 5G radio access system are a systemcapacity 1000 times as high as, a data transmission rate 100 times ashigh as, a data latency one tenth ( 1/10) as low as, and simultaneouslyconnected communication terminals 100 times as many as those in the LTEsystem, to further reduce the power consumption and device cost.

In order to satisfy such requirements, techniques for enabling spatialmultiplexing such as multiple-input multiple-output (MIMO) andbeamforming using multi-element antennas are being studied to increasethe data transmission capacity using frequencies over a wide frequencyrange as well as to increase the data transmission rate through increasein spectral efficiency.

In the MIMO and the beamforming using multi-element antennas, phases andoutputs of the respective antenna elements included in a multi-elementantenna are set and adjusted. Thus, the set accuracy of the phases andthe outputs of the respective antenna elements influences theperformance. Here, the multi-element antenna is calibrated to increasethe set accuracy of the phases and the outputs of the respective antennaelements.

The rotating element electric field vector (REV) method (see Non-PatentDocument 10) and the relative calibration (see Non-Patent Document 11)are being studied as methods for calibrating the multi-element antenna.Furthermore, the self-calibration method (see Non-Patent Document 12)and the Over-The-Air (OTA) method (see Non-Patent Document 13) are beingstudied as calibration execution methods.

PRIOR-ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: 3GPP TS36.300 V12.4.0-   Non-Patent Document 2: 3GPP S1-083461-   Non-Patent Document 3: 3GPP R2-082899-   Non-Patent Document 4: 3GPP TR 36.814 V9.0.0-   Non-Patent Document 5: 3GPP TR 36.912 V10.0.0-   Non-Patent Document 6: 3GPP TR 36.819 V11.2.0-   Non-Patent Document 7: 3GPP TS 36.141 V12.6.0-   Non-Patent Document 8: 3GPP TR36.842 V12.0.0-   Non-Patent Document 9: “Scenarios, requirements and KPIs for 5G    mobile and wireless system”, [online], Apr. 30, 2013,    ICT-317669-METIS/D1.1, [Searched on Apr. 2, 2015], Internet    <https://www.metis2020.com/documents/deliverables/>-   Non-Patent Document 10: Seiji MANO, Takashi KATAGI, “A Method for    Measuring Amplitude and Phase of Each Radiating Element of a Phased    Array Antenna, Rotating Element Electric Field Vector Method”, The    Transactions of the Institute of Electronics and Communication    Engineers of Japan, B, Vol. J65-B, No. 5, pp. 555-560, May 1982-   Non-Patent Document 11: Yoshitaka HARA, Yasuhiro YANO, Hiroshi KUBO,    “Antenna Calibration Using Frequency Selection in OFDMA/TDD    Systems”, IEICE Technical Report RCS2007-143, January 2008-   Non-Patent Document 12: Yasunori NOUDA, Yoshitaka HARA, Yasuhiro    YANO, Hiroshi KUBO, “An Antenna Array Auto-Calibration Method with    Bidirectional Channel Measurement for TDD Systems”, IEICE Technical    Report RCS2008-12, May 2008-   Non-Patent Document 13: X. Hou, et al, “Experimental Study of    Advanced MU-MIMO Scheme with Antenna Calibration for the Evolving    LTE TDD System”, IEEE 23rd PIMRC, 2012

SUMMARY Problems to be Solved by the Invention

In the MIMO and the beamforming using multi-element antennas, thethroughput of the multi-element antennas needs to be improved. However,the following problems lie in improving the throughput of themulti-element antennas.

The first point will be described below. Without matching phase andamplitude differences among the antenna elements, problems occur whichinclude: (a) uncontrollable beam directivity with which beams cannot bedirected in a desired direction; (b) decrease in gain expressed by, forexample, equivalent isotropic radiated power (abbreviated as EIRP); and(c) increase in side lobe power which increases interference with otherusers. Particularly, accuracy is required in MIMO transmission forcontrolling null points.

The second point will be described below. It is necessary to eliminatetemperature and temporal variations in phase and amplitude differencesamong the antenna elements. However, since broadband communicationincreases the frequency bandwidth, an amplifier and a filter, etc. causea problem of significantly influencing amounts of the temperature andtemporal variations.

Unlike the conventional configurations in which an amplifier and afilter are placed in an indoor room with temperature control andconnected to an antenna outdoor through cables for extension, outdoorinstallation of an amplifier, for example, an active phased arrayantenna (APAA) is being studied. Since the temperature variationsincrease in such a case, the calibration in operation is important.

The object of the present invention is to provide a communication systemcapable of calibration with higher accuracy to match phase and amplitudedifferences in beam among a plurality of antenna elements included in amulti-element antenna and capable of communication with a relativelyhigh throughput.

Means to Solve the Problems

The communication system according to the present invention is acommunication system including a base station device and a communicationterminal device between which a signal is transmitted and receivedthrough a multi-element antenna including a plurality of antennaelements, wherein at least one of the base station device and thecommunication terminal device includes a calibration unit that performscalibration of phases and amplitudes of beams formed by the antennaelements when the signal is transmitted and received, and thecalibration unit obtains a correction value for the phases and theamplitudes of the beams in the respective antenna elements so that thephases and the amplitudes of the beams are identical among the antennaelements, and performs the calibration based on the obtained correctionvalue.

Effects of the Invention

The communication system according to the present invention is acommunication system including a base station device and a communicationterminal device. A signal is transmitted and received between the basestation device and the communication terminal device through amulti-element antenna including a plurality of antenna elements. Atleast one of the base station device and the communication terminaldevice includes a calibration unit. The calibration unit performscalibration of phases and amplitudes of beams formed by the antennaelements when the signal is transmitted and received. The calibrationunit obtains a correction value for the phases and the amplitudes of thebeams in the respective antenna elements so that the phases and theamplitudes of the beams are identical among the antenna elements, andperforms the calibration based on the obtained correction value. Sincethe calibration can be performed with higher accuracy, it is possible tomatch phase and amplitude differences in beam among a plurality ofantenna elements included in a multi-element antenna. Thus, acommunication system capable of communication with a relatively highthroughput can be implemented.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a radio frame foruse in an LTE communication system.

FIG. 2 is a block diagram showing the overall configuration of an LTEcommunication system 200 under discussion of 3GPP.

FIG. 3 is a block diagram showing the configuration of a user equipment202 shown in FIG. 2, which is a communication terminal according to thepresent invention.

FIG. 4 is a block diagram showing the configuration of a base station203 shown in FIG. 2, which is a base station according to the presentinvention.

FIG. 5 is a block diagram showing the configuration of an MME accordingto the present invention.

FIG. 6 is a flowchart showing an outline from a cell search to an idlestate operation performed by a communication terminal (UE) in the LTEcommunication system.

FIG. 7 shows the concept of a cell configuration when macro eNBs andsmall eNBs coexist.

FIG. 8 is a block diagram illustrating a configuration of acommunication apparatus in a communication system according to a firstembodiment of the present invention.

FIG. 9 is a block diagram illustrating an example configuration of a PHYprocessing unit 901, a control unit 9411, and n antenna elements 909,922, . . . , and 935.

FIG. 10 is a block diagram illustrating the example configuration of thePHY processing unit 901, the control unit 9411, and the n antennaelements 909, 922, . . . , and 935.

FIG. 11 is a block diagram illustrating an example configuration of thePHY processing unit 901, the control unit 9411, and the n antennaelements 909, 922, . . . , and 935.

FIG. 12 is a block diagram illustrating the example configuration of thePHY processing unit 901, the control unit 9411, and the n antennaelements 909, 922, . . . , and 935.

FIG. 13 is a block diagram illustrating another example configuration ofa PHY processing unit 901A, a control unit 9412, and the n antennaelements 909, 922, . . . , and 935.

FIG. 14 is a block diagram illustrating the other example configurationof the PHY processing unit 901A, the control unit 9412, and the nantenna elements 909, 922, . . . , and 935.

FIG. 15 is a block diagram illustrating another example configuration ofthe PHY processing unit 901A, the control unit 9412, and the n antennaelements 909, 922, . . . , and 935.

FIG. 16 is a block diagram illustrating the other example configurationof the PHY processing unit 901A, the control unit 9412, and the nantenna elements 909, 922, . . . , and 935.

FIG. 17 illustrates example mapping in transmission data of a firstantenna element.

FIG. 18 illustrates example mapping in transmission data of a secondantenna element to an n-th antenna element.

FIG. 19 illustrates examples of mapping and the reception power at eachfrequency, in transmission data of the first antenna element.

FIG. 20 illustrates another example mapping in the transmission data ofthe first antenna element.

FIG. 21 illustrates another example mapping in the transmission data ofthe second antenna element to the n-th antenna element.

FIG. 22 further illustrates another example mapping in the transmissiondata of the first antenna element.

FIG. 23 further illustrates another example mapping in the transmissiondata of the second antenna element.

FIG. 24 further illustrates another example mapping in the transmissiondata of the third antenna element.

FIG. 25 further illustrates another example mapping in the transmissiondata of the fourth antenna element.

FIG. 26 further illustrates another example mapping of transmission datain the transmission data of the first antenna element.

FIG. 27 further illustrates another example mapping in the transmissiondata of the second antenna element to the n-th antenna element.

FIG. 28 is a flowchart indicating an example procedure on calibrationprocesses in a communication system according to a fourth embodiment.

FIG. 29 is a flowchart indicating an example procedure on calibrationprocesses in a communication system according to a first modification ofthe fourth embodiment.

FIG. 30 is a flowchart indicating an example procedure on calibrationprocesses in a communication system according to a second modificationof the fourth embodiment.

FIG. 31 is a flowchart indicating an example procedure on calibrationprocesses in a communication system according to a third modification ofthe fourth embodiment.

FIG. 32 illustrates an example sequence on calibration in acommunication system according to a fifth embodiment.

FIG. 33 illustrates another example sequence on calibration in thecommunication system according to the fifth embodiment.

FIG. 34 illustrates an example configuration of a subframe when cal-RSsare mapped to a physical downlink shared channel region.

FIG. 35 illustrates another example configuration of a subframe whencal-RSs are mapped to a physical downlink shared channel region.

FIG. 36 illustrates an example configuration of a subframe when cal-RSsare mapped to an MBSFN region.

FIG. 37 illustrates an example configuration of a subframe when cal-RSsare mapped to an ABS region.

FIG. 38 illustrates an example configuration of a subframe when cal-RSsof each antenna group are mapped to a physical downlink shared channelregion according to a seventh embodiment.

FIG. 39 illustrates an example configuration of a subframe when cal-RSsare mapped to a part of the frequency axis in a physical downlink sharedchannel region according to an eighth embodiment.

FIG. 40 illustrates another example configuration of a subframe whencal-RSs are mapped to a part of the frequency axis in a physicaldownlink shared channel region according to the eighth embodiment.

FIG. 41 illustrates an example configuration of a subframe when cal-RSsfor each antenna group are mapped to a part of the frequency axis in aphysical downlink shared channel region according to the eighthembodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 2 is a block diagram showing an overall configuration of an LTEcommunication system 200, which is under discussion of 3GPP. FIG. 2 willbe described. A radio access network is referred to as an evolveduniversal terrestrial radio access network (E-UTRAN) 201. A userequipment device (hereinafter, referred to as a “user equipment (UE)”)202 that is a communication terminal device is capable of radiocommunication with a base station device (hereinafter, referred to as a“base station (E-UTRAN Node B: eNB)”) 203 and transmits and receivessignals through radio communication.

Here, the “communication terminal device” covers not only a userequipment device such as a movable mobile phone terminal device, butalso an unmovable device such as a sensor. In the following description,the “communication terminal device” may be simply referred to as a“communication terminal”.

The E-UTRAN is composed of one or a plurality of base stations 203,provided that a control protocol for the user equipment 202 such as aradio resource control (RRC), and user planes such as a packet dataconvergence protocol (PDCP), radio link control (RLC), medium accesscontrol (MAC), or physical layer (PHY) are terminated in the basestation 203.

The control protocol radio resource control (RRC) between the userequipment 202 and the base station 203 performs broadcast, paging, RRCconnection management, and the like. The states of the base station 203and the user equipment 202 in RRC are classified into RRC IDLE and RRCCONNECTED.

In RRC IDLE, public land mobile network (PLMN) selection, systeminformation (SI) broadcast, paging, cell re-selection, mobility, and thelike are performed. In RRC CONNECTED, the user equipment has RRCconnection and is capable of transmitting and receiving data to and froma network. In RRC CONNECTED, for example, handover (HO) and measurementof a neighbor cell are performed.

The base stations 203 are classified into eNBs 207 and Home-eNBs 206.The communication system 200 includes an eNB group 203-1 including aplurality of eNBs 207 and a Home-eNB group 203-2 including a pluralityof Home-eNBs 206. A system, composed of an evolved packet core (EPC)being a core network and an E-UTRAN 201 being a radio access network, isreferred to as an evolved packet system (EPS). The EPC being a corenetwork and the E-UTRAN 201 being a radio access network may becollectively referred to as a “network”.

The eNB 207 is connected to an MME/S-GW unit (hereinafter, also referredto as an “MME unit”) 204 including a mobility management entity (MME), aserving gateway (S-GW), or an MME and an S-GW by means of an S1interface, and control information is communicated between the eNB 207and the MME unit 204. A plurality of MME units 204 may be connected toone eNB 207. The eNBs 207 are connected to each other by means of an X2interface, and control information is communicated between the eNBs 207.

The Home-eNB 206 is connected to the MME unit 204 by means of an S1interface, and control information is communicated between the Home-eNB206 and the MME unit 204. A plurality of Home-eNBs 206 are connected toone MME unit 204. Or, the Home-eNBs 206 are connected to the MME units204 through a Home-eNB gateway (HeNBGW) 205. The Home-eNB 206 isconnected to the HeNBGW 205 by means of an S1 interface, and the HeNBGW205 is connected to the MME unit 204 by means of an S1 interface.

One or a plurality of Home-eNBs 206 are connected to one HeNBGW 205, andinformation is communicated therebetween through an S1 interface. TheHeNBGW 205 is connected to one or a plurality of MME units 204, andinformation is communicated therebetween through an S1 interface.

The MME units 204 and HeNBGW 205 are entities of higher layer,specifically, higher nodes, and control the connections between the userequipment (UE) 202 and the eNB 207 and the Home-eNB 206 being basestations. The MME units 204 configure an EPC being a core network. Thebase station 203 and the HeNBGW 205 configure the E-UTRAN 201.

Further, 3GPP is studying the configuration below. The X2 interfacebetween the Home-eNBs 206 is supported. In other words, the Home-eNBs206 are connected to each other by means of an X2 interface, and controlinformation is communicated between the Horne-eNBs 206. The HeNBGW 205appears to the MME unit 204 as the Home-eNB 206. The HeNBGW 205 appearsto the Home-eNB 206 as the MME unit 204.

The interfaces between the Home-eNBs 206 and the MME units 204 are thesame, which are the S1 interfaces, in both cases where the Home-eNB 206is connected to the MME unit 204 through the HeNBGW 205 and it isdirectly connected to the MME unit 204.

The base station device 203 may configure a single cell or a pluralityof cells. Each cell has a range predetermined as a coverage in which thecell can communicate with the user equipment 202 and performs radiocommunication with the user equipment 202 within the coverage. In thecase where one base station device 203 configures a plurality of cells,every cell is configured so as to communicate with the user equipment202.

FIG. 3 is a block diagram showing the configuration of the userequipment 202 of FIG. 2 that is a communication terminal according tothe present invention. The transmission process of the user equipment202 shown in FIG. 3 will be described. First, a transmission data bufferunit 303 stores the control data from a protocol processing unit 301 andthe user data from an application unit 302. The data stored in thetransmission data buffer unit 303 is passed to an encoding unit 304 andis subjected to an encoding process such as error correction. There mayexist the data output from the transmission data buffer unit 303directly to a modulating unit 305 without the encoding process. The dataencoded by the encoding unit 304 is modulated by the modulating unit305. The modulated data is converted into a baseband signal, and thebaseband signal is output to a frequency converting unit 306 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 307 to the basestation 203.

The user equipment 202 executes the reception process as follows. Theradio signal from the base station 203 is received through the antenna307. The received signal is converted from a radio reception frequencyinto a baseband signal by the frequency converting unit 306 and is thendemodulated by a demodulating unit 308. The demodulated data is passedto a decoding unit 309 and is subjected to a decoding process such aserror correction. Among the pieces of decoded data, the control data ispassed to the protocol processing unit 301, and the user data is passedto the application unit 302. A series of processes by the user equipment202 is controlled by a control unit 310. This means that, though notshown in FIG. 3, the control unit 310 is connected to the individualunits 301 to 309.

FIG. 4 is a block diagram showing the configuration of the base station203 of FIG. 2 that is a base station according to the present invention.The transmission process of the base station 203 shown in FIG. 4 will bedescribed. An EPC communication unit 401 performs data transmission andreception between the base station 203 and the EPC (such as the MME unit204), HeNBGW 205, and the like. A communication with another basestation unit 402 performs data transmission and reception to and fromanother base station. The EPC communication unit 401 and thecommunication with another base station unit 402 each transmit andreceive information to and from a protocol processing unit 403. Thecontrol data from the protocol processing unit 403, and the user dataand the control data from the EPC communication unit 401 and thecommunication with another base station unit 402 are stored in atransmission data buffer unit 404.

The data stored in the transmission data buffer unit 404 is passed to anencoding unit 405 and is then subjected to an encoding process such aserror correction. There may exist the data output from the transmissiondata buffer unit 404 directly to a modulating unit 406 without theencoding process. The encoded data is modulated by the modulating unit406. The modulated data is converted into a baseband signal, and thebaseband signal is output to a frequency converting unit 407 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 408 to one or aplurality of user equipments 202.

The reception process of the base station 203 is executed as follows. Aradio signal from one or a plurality of user equipments 202 is receivedthrough the antenna 408. The received signal is converted from a radioreception frequency into a baseband signal by the frequency convertingunit 407, and is then demodulated by a demodulating unit 409. Thedemodulated data is passed to a decoding unit 410 and is then subjectedto a decoding process such as error correction. Among the pieces ofdecoded data, the control data is passed to the protocol processing unit403, the EPC communication unit 401, or the communication with anotherbase station unit 402, and the user data is passed to the EPCcommunication unit 401 and the communication with another base stationunit 402. A series of processes by the base station 203 is controlled bya control unit 411. This means that, though not shown in FIG. 4, thecontrol unit 411 is connected to the individual units 401 to 410.

FIG. 5 is a block diagram showing the configuration of the MME accordingto the present invention. FIG. 5 shows the configuration of an MME 204 aincluded in the MME unit 204 shown in FIG. 2 described above. A PDN GWcommunication unit 501 performs data transmission and reception betweenthe MME 204 a and the PDN GW. A base station communication unit 502performs data transmission and reception between the MME 204 a and thebase station 203 by means of the S1 interface. In the case where thedata received from the PDN GW is user data, the user data is passed fromthe PDN GW communication unit 501 to the base station communication unit502 via a user plane communication unit 503 and is then transmitted toone or a plurality of base stations 203. In the case where the datareceived from the base station 203 is user data, the user data is passedfrom the base station communication unit 502 to the PDN GW communicationunit 501 via the user plane communication unit 503 and is thentransmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is passed from the PDN GW communication unit 501 to acontrol plane control unit 505. In the case where the data received fromthe base station 203 is control data, the control data is passed fromthe base station communication unit 502 to the control plane controlunit 505.

A HeNBGW communication unit 504 is provided in the case where the HeNBGW205 is provided, which performs data transmission and reception betweenthe MME 204 a and the HeNBGW 205 by means of the interface (IF)according to an information type. The control data received from theHeNBGW communication unit 504 is passed from the HeNBGW communicationunit 504 to the control plane control unit 505. The processing resultsof the control plane control unit 505 are transmitted to the PDN GW viathe PDN GW communication unit 501. The processing results of the controlplane control unit 505 are transmitted to one or a plurality of basestations 203 by means of the S1 interface via the base stationcommunication unit 502, and are transmitted to one or a plurality ofHeNBGWs 205 via the HeNBGW communication unit 504.

The control plane control unit 505 includes a NAS security unit 505-1,an SAE bearer control unit 505-2, and an idle state mobility managingunit 505-3, and performs an overall process for the control plane. TheNAS security unit 505-1 provides, for example, security of a non-accessstratum (NAS) message. The SAE bearer control unit 505-2 manages, forexample, a system architecture evolution (SAE) bearer. The idle statemobility managing unit 505-3 performs, for example, mobility managementof an idle state (LTE-IDLE state, which is merely referred to as idle aswell), generation and control of a paging signal in the idle state,addition, deletion, update, and search of a tracking area of one or aplurality of user equipments 202 being served thereby, and tracking arealist management.

The MME 204 a distributes a paging signal to one or a plurality of basestations 203. In addition, the MME 204 a performs mobility control of anidle state. When the user equipment is in the idle state and an activestate, the MME 204 a manages a list of tracking areas. The MME 204 abegins a paging protocol by transmitting a paging message to the cellbelonging to a tracking area in which the UE is registered. The idlestate mobility managing unit 505-3 may manage the CSG of the Home-eNBs206 to be connected to the MME 204 a, CSG IDs, and a whitelist.

An example of a cell search method in a mobile communication system willbe described next. FIG. 6 is a flowchart showing an outline from a cellsearch to an idle state operation performed by a communication terminal(UE) in the LTE communication system. When starting a cell search, inStep ST601, the communication terminal synchronizes slot timing andframe timing by a primary synchronization signal (P-SS) and a secondarysynchronization signal (S-SS) transmitted from a neighbor base station.

The P-SS and S-SS are collectively referred to as a synchronizationsignal (SS). Synchronization codes, which correspond one-to-one to PCIsassigned per cell, are assigned to the synchronization signals (SSs).The number of PCIs is currently studied in 504 ways. The 504 ways ofPCIs are used for synchronization, and the PCIs of the synchronizedcells are detected (specified).

In Step ST602, next, the user equipment detects a cell-specificreference signal (CRS) being a reference signal (RS) transmitted fromthe base station per cell and measures the reference signal receivedpower (RSRP). The codes corresponding one-to-one to the PCIs are usedfor the reference signal RS. Separation from another cell is enabled bycorrelation using the code. The code for RS of the cell is derived fromthe PCI specified in Step ST601, so that the RS can be detected and theRS received power can be measured.

In Step ST603, next, the user equipment selects the cell having the bestRS received quality, for example, the cell having the highest RSreceived power, that is, the best cell, from one or more cells that havebeen detected up to Step ST602.

In Step ST604, next, the user equipment receives the PBCH of the bestcell and obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas a transmission bandwidth configuration (dl-bandwidth)), the number oftransmission antennas, and a system frame number (SFN).

In Step ST605, next, the user equipment receives the DL-SCH of the cellbased on the cell configuration information of the MIB, to therebyobtain a system information block (SIB) 1 of the broadcast informationBCCH. The SIB1 contains the information about the access to the cell,information about cell selection, and scheduling information on anotherSIB (SIBk; k is an integer equal to or greater than two). In addition,the SIB1 contains a tracking area code (TAC).

In Step ST606, next, the communication terminal compares the TAC of theSIB1 received in Step ST605 with the TAC portion of a tracking areaidentity (TAI) in the tracking area list that has already been possessedby the communication terminal. The tracking area list is also referredto as a TAI list. TAI is the identification information for identifyingtracking areas and is composed of a mobile country code (MCC), a mobilenetwork code (MNC), and a tracking area code (TAC). MCC is a countrycode. MNC is a network code. TAC is the code number of a tracking area.

If the result of the comparison of Step ST606 shows that the TACreceived in Step ST605 is identical to the TAC included in the trackingarea list, the user equipment enters an idle state operation in thecell. If the comparison shows that the TAC received in Step ST605 is notincluded in the tracking area list, the communication terminal requiresa core network (EPC) including MME and the like to change a trackingarea through the cell for performing tracking area update (TAU).

The device configuring a core network (hereinafter, also referred to asa “core-network-side device”) updates the tracking area list based on anidentification number (such as UE-ID) of a communication terminaltransmitted from the communication terminal together with a TAU requestsignal. The core-network-side device transmits the updated tracking arealist to the communication terminal. The communication terminal rewrites(updates) the TAC list of the communication terminal based on thereceived tracking area list. After that, the communication terminalenters the idle state operation in the cell.

Widespread use of smartphones and tablet terminal devices explosivelyincreases traffic in cellular radio communications, causing a fear ofinsufficient radio resources all over the world. To increase spectralefficiency, thus, it is studied to downsize cells for further spatialseparation.

In the conventional configuration of cells, the cell configured by aneNB has a relatively-wide-range coverage. Conventionally, cells areconfigured such that relatively-wide-range coverages of a plurality ofcells configured by a plurality of macro eNBs cover a certain area.

When cells are downsized, the cell configured by an eNB has anarrow-range coverage compared with the coverage of a cell configured bya conventional eNB. Thus, in order to cover a certain area as in theconventional case, a larger number of downsized eNBs than theconventional eNBs are required.

In the description below, a “macro cell” refers to a cell having arelatively wide coverage, such as a cell configured by a conventionaleNB, and a “macro eNB” refers to an eNB configuring a macro cell. A“small cell” refers to a cell having a relatively narrow coverage, suchas a downsized cell, and a “small eNB” refers to an eNB configuring asmall cell.

The macro eNB may be, for example, a “wide area base station” describedin Non-Patent Document 7.

The small eNB may be, for example, a low power node, local area node, orhotspot. Alternatively, the small eNB may be a pico eNB configuring apico cell, a femto eNB configuring a femto cell, HeNB, remote radio head(RRH), remote radio unit (RRU), remote radio equipment (RRE), or relaynode (RN). Still alternatively, the small eNB may be a “local area basestation” or “home base station” described in Non-Patent Document 7.

FIG. 7 shows the concept of the cell configuration in which macro eNBsand small eNBs coexist. The macro cell configured by a macro eNB has arelatively-wide-range coverage 701. A small cell configured by a smalleNB has a coverage 702 whose range is narrower than that of the coverage701 of a macro eNB (macro cell).

When a plurality of eNBs coexist, the coverage of the cell configured byan eNB may be included in the coverage of the cell configured by anothereNB. In the cell configuration shown in FIG. 7, as indicated by areference “704” or “705”, the coverage 702 of the small cell configuredby a small eNB may be included in the coverage 701 of the macro cellconfigured by a macro eNB.

As indicated by the reference “705”, the coverages 702 of a pluralityof, for example, two small cells may be included in the coverage 701 ofone macro cell. A user equipment (UE) 703 is included in, for example,the coverage 702 of the small cell and performs communication via thesmall cell.

In the cell configuration shown in FIG. 7, as indicated by a reference“706”, the coverage 701 of the macro cell configured by a macro eNB mayoverlap the coverages 702 of the small cells configured by small eNBs ina complicated manner.

As indicated by a reference “707”, the coverage 701 of the macro cellconfigured by a macro eNB may not overlap the coverages 702 of the smallcells configured by small eNBs.

Further, as indicated by a reference “708”, the coverages 702 of a largenumber of small cells configured by a large number of small eNBs may beconfigured in the coverage 701 of one macro cell configured by one macroeNB.

The following problems (1) and (2) lie in improving the throughput ofthe multi-element antennas.

(1) Without matching phase and amplitude differences among the antennaelements, problems occur which include: (a) uncontrollable beamdirectivity with which beams cannot be directed in a desired direction;(b) decrease in gain expressed by, for example, equivalent isotropicradiated power (abbreviated as EIRP); and (c) increase in side lobepower which increases interference with other users.

(2) It is necessary to eliminate temperature and temporal variations inphase and amplitude differences among the antenna elements. However,since broadband communication increases the frequency bandwidth, anamplifier and a filter, etc. cause a problem of significantlyinfluencing amounts of the temperature and temporal variations.

The first embodiment will disclose a method for calibration with higheraccuracy to match phase and amplitude differences in beam among aplurality of antenna elements included in a multi-element antenna.

FIG. 8 is a block diagram illustrating a configuration of acommunication apparatus in a communication system according to the firstembodiment of the present invention. The communication apparatus may bea base station or a user equipment. In other words, the communicationsystem according to the first embodiment includes a base station and auser equipment, and at least one of the base station and the userequipment is embodied by the communication apparatus in FIG. 8.

The communication apparatus includes a physical layer (PHY) processingunit 801, a plurality of antenna elements 802 to 805, and a control unit806. The plurality of antenna elements 802 to 805 are n antenna elements802 to 805 (n is a natural number), specifically, a first antennaelement 802, a second antenna element 803, a third antenna element 804,. . . , and an n-th antenna element 805. The first antenna element 802to the n-th antenna element 805 are connected to the PHY processing unit801. The first antenna element 802 to the n-th antenna element 805 forma multi-element antenna.

The PHY processing unit 801 performs, according to an instruction givenfrom the control unit 806, respective processes of generating atransmission signal, mapping, extracting a reception signal, anddemapping. The control unit 806 controls timing on transmission andreception, allocation of time resources, frequency resources, and coderesources, transmission power, and a phase value and an amplitude valuefor the antenna elements.

The PHY processing unit 801 corresponds to a calibration unit thatcalibrates phases and amplitudes of beams formed by the antenna elements802 to 805, upon transmission and reception of a signal. The PHYprocessing unit 801 obtains a correction value for the phases and theamplitudes of the beams in the respective antenna elements 802 to 805 sothat the phases and the amplitudes of the beams are identical among theantenna elements 802 to 805, and calibrates the phases and theamplitudes based on the obtained correction value.

Next, an example procedure of the control processes in the communicationapparatus will be described with the signal flow. The control unit 806determines whether calibration is necessary. When determining thatcalibration is necessary, the control unit 806 determines timing, afrequency, and the transmission power for the calibration, and notifiesthe PHY processing unit 801 of these.

Specifically, the PHY processing unit 801 performs the calibration asfollows. The PHY processing unit 801 maps calibration RSs (may behereinafter referred to as “cal-RSs”), sets a transmission power value,and transmits a signal with predetermined timing using a predeterminedantenna element according to an instruction given from the control unit806.

Furthermore, the PHY processing unit 801 causes a predetermined antennaelement to receive the transmitted signal, according to an instructiongiven from the control unit 806. The PHY processing unit 801 demapscalibration RSs from the received signal, calculates propagationproperties from the value obtained from the demapping, and notifies thecontrol unit 806 of the propagation properties.

The control unit 806 analyzes relative values of the antenna elements802 to 805 or differences with an ideal value of the propagationproperties measured in an anechoic chamber in advance, for example,before shipment, calculates a correction value for the phases and theamplitudes of the antenna elements 802 to 805 from the analyzed valuesor the difference values, and notifies the PHY processing unit 801 ofthe correction value.

The PHY processing unit 801 sets the correction value given from thecontrol unit 806 so that an offset is added to the subsequent signals.

Whether the control unit 806 needs to perform calibration may bedetermined through periodically (on a regular basis) executing theprocesses by the control unit 806 and the PHY processing unit 801 asdescribed above, based on a difference between a currently set value anda result of the correction value that is calculated by the control unit806 for the phases and the amplitudes of the antenna elements 802 to805.

When the communication apparatus is a base station, the communicationapparatus may start calibration according to an instruction from amaintenance management apparatus in high layer. Accordingly, themaintenance management apparatus in high layer, for example, prevents asituation where a plurality of base stations overlapping in cellcoverage thereof simultaneously perform calibration (may be hereinafterreferred to as a “calibration situation”), and can avoid occurrence of anon-service area.

Similarly, when a base station that is a communication apparatusreceives notification indicating whether the surrounding base stationsare in a calibration situation from themselves and the surrounding basestations are not yet in the calibration situation, the own base stationmay start calibration. Conversely, the base station may notify thesurrounding base stations of whether the own base station is in acalibration situation.

Alternatively, when the base station is provided with a temperaturesensor and the temperature variations become larger than or equal to apredetermined value, the base station may start calibration.Transmission power amplifiers, phasers, and filters that separate andextract a required frequency have temperature characteristics, and thus,the transmission power amplifiers, the phasers, and the filters areknown for having respective variations. Inaccuracy of the beam controlsubject to the variations in the transmission power amplifiers, thephasers, and the filters can be corrected by causing the base station tostart calibration when the temperature variations become larger than orequal to a predetermined value as described above.

Alternatively, the communication apparatus may start calibrationaccording to a request from a corresponding apparatus. When thecommunication apparatus is a base station and the correspondingapparatus is a base station or a repeater, the corresponding apparatusknows or can learn a carrier to noise ratio (abbreviated as CNR) or asignal to noise ratio (abbreviated as SNR) for use in a normal operationwith appropriate directivity. Thus, the corresponding apparatus mayinstruct the communication apparatus to start calibration, for example,when the CNR or the SNR is smaller than or equal to a predeterminedvalue due to the temperature and temporal variations, etc.

When a user equipment for calibration is provided, more specifically,when a user equipment is always placed at a specific position or when auser equipment moved to a specific position is determined as a userequipment for calibration, the user equipment may instruct acommunication apparatus to start calibration as described above.

Alternatively, a user equipment transmits, to an evolved packet core(EPC), quality information such as received power and the SNR as well asGlobal Positioning System (GPS) position information collected using,for example, a minimum drive test (MDT) function. Then, if the EPCdetects a difference with the normal operation based on the receivedquality information and there is the difference, the EPC may notify aninstruction to start calibration to the base station.

Particularly, in a transmission system, for example, the control unit806 may set a correction value for a phase and an amplitude of thetransmission system by handling the timing to execute calibration as thetiming with which the transmission system does not transmit data forcommunication with the corresponding apparatus. Furthermore, in areception system, the control unit 806 may set a correction value for aphase and an amplitude of the reception system by handling the timing toexecute calibration as the timing with which the reception system hasnot received data for communication with the corresponding apparatus. Intime division duplex (abbreviated as TDD), calibration may be performedduring a gap duration that is a switching time between transmission andreception.

Furthermore, the control unit 806 may limit frequencies at whichcalibration is to be executed to a part of the frequencies, that is, toa sub-band. Accordingly, normal communication (service) is possible witha resource that has not been calibrated. Furthermore, when it is clearthat, for example, the transmission power amplifiers, the phasers, andthe filters have little variations in the temperature, etc., calibrationis not required at the sub-band at which they have been calibrated, andthe performance can be guaranteed by interpolation.

Similarly, calibration at the sub-band before increase in thetemperature variations can guarantee the performance.

Furthermore, when the antenna elements have various distances, thecontrol unit 806 divides the antenna elements into several groupsaccording to the distances, and increases the transmission power for agroup of relatively distant antenna elements more than that of a groupof relatively close antenna elements, which improves the SNR and thus iseffective. Here, some of the antenna elements may belong to a pluralityof groups.

Furthermore, no correction by the control unit 806 is also effectivewhen a value is significantly different from a calibration valuemeasured in, for example, an anechoic chamber, before shipment or fromcorrection values in the past record. For example, when a large truckpasses right in front, normal calibration is possible by skipping thecurrent calibration and performing the next calibration.

Furthermore, when the correction value exceeds a change acceptable valuethat is the largest value up to which change is acceptable, multipath isdetected and separated. When calibration is performed only withprincipal waves and a value falls within the acceptable values,calibration with the value is also effective. Such a calibration iseffective, for example, when a large sign is placed closer and multipathnormally occurs.

Example signal flows of the PHY processing unit 801 and the control unit806 will be described with reference to FIGS. 9 and 10. FIGS. 9 and 10are block diagrams illustrating an example configuration of a PHYprocessing unit 901, a control unit 9411, and n antenna elements 909,922, . . . , and 935. FIGS. 9 and 10 are connected across a border BL1.

The PHY processing unit 901 includes a plurality of encoder units, aplurality of modulating units, a plurality of switching units, aplurality of demodulating units, a plurality of decoder units. The PHYprocessing unit 901 corresponds to a calibration unit.

The plurality of encoder units are n encoder units (n is a naturalnumber) consisting of, specifically, a first encoder unit 902, a secondencoder unit 915, . . . , and an n-th encoder unit 928. The plurality ofmodulating units are n modulating units (n is a natural number)consisting of, specifically, a first modulating unit 907, a secondmodulating unit 920, . . . , and an n-th modulating unit 933. Theplurality of switching units are n switching units (n is a naturalnumber) consisting of, specifically, a first switching unit 908, asecond switching unit 921, . . . , and an n-th switching unit 934.

The plurality of demodulating units are n demodulating units (n is anatural number) consisting of, specifically, a first demodulating unit910, a second demodulating unit 923, . . . , and an n-th demodulatingunit 936. The plurality of decoder units are n decoder units (n is anatural number) consisting of, specifically, a first decoder unit 911, asecond decoder unit 924, . . . , and an n-th decoder unit 937.

Furthermore, a plurality of antenna elements, specifically, the nantenna elements (n is a natural number) consisting of the first antennaelement 909, the second antenna element 922, . . . , and the n-thantenna element 935 are provided to correspond to the plurality ofencoder units 902, 915, . . . , and 928, and the plurality of decoderunits 911, 924, . . . , and 937, respectively.

The first encoder unit 902 includes a first transmission data generatingunit 903, a first calibration RS mapping unit 904, a first transmissionpower setting unit 905, and a first transmission correction processingunit 9061. The first decoder unit 911 includes a first receptioncorrection processing unit 9121, a first calibration RS extracting unit913, and a first response characteristics calculating unit 914.

The second encoder unit 915 includes a second transmission datagenerating unit 916, a second calibration RS mapping unit 917, a secondtransmission power setting unit 918, and a second transmissioncorrection processing unit 9191. The second decoder unit 924 includes asecond reception correction processing unit 9251, a second calibrationRS extracting unit 926, and a second response characteristicscalculating unit 927.

The n-th encoder unit 928 includes an n-th transmission data generatingunit 929, an n-th calibration RS mapping unit 930, an n-th transmissionpower setting unit 931, and an n-th transmission correction processingunit 9321. The n-th decoder unit 937 includes an n-th receptioncorrection processing unit 9381, an n-th calibration RS extracting unit939, and an n-th response characteristics calculating unit 940.

In FIGS. 9 and 10, the first encoder unit 902, the first modulating unit907, the first switching unit 908, and the first antenna element 909form a first transmission system. The second encoder unit 915, thesecond modulating unit 920, the second switching unit 921, and thesecond antenna element 922 form a second transmission system. The n-thencoder unit 928, the n-th modulating unit 933, the n-th switching unit934, and the n-th antenna element 935 form an n-th transmission system.

In FIGS. 9 and 10, the first antenna element 909, the first switchingunit 908, the first demodulating unit 910, and the first decoder unit911 form a first reception system. The second antenna element 922, thesecond switching unit 921, the second demodulating unit 923, and thesecond decoder unit 924 form a second reception system. The n-th antennaelement 935, the n-th switching unit 934, the n-th demodulating unit936, and the n-th decoder unit 937 form an n-th reception system.

FIGS. 9 and 10 illustrate an example relative calibration in TDDsystems. In the example of FIGS. 9 and 10, the first transmission systemmakes a transmission, and the second to the n-th reception systemsreceive the transmission to calculate response characteristics in thesecond to the n-th reception systems.

When the control unit 9411 determines to execute calibration, the PHYprocessing unit 901 performs the following processes according to aninstruction from the control unit 9411.

The first transmission data generating unit 903 generates transmissiondata, and gives it to the first calibration RS mapping unit 904. Thefirst calibration RS mapping unit 904 maps (inserts) cal-RSs to betransmitted with the timing and at the frequency that are instructedfrom the control unit 9411, to the transmission data given from thefirst transmission data generating unit 903. The first calibration RSmapping unit 904 gives the first transmission power setting unit 905 thetransmission data to which the cal-RSs are mapped.

The first transmission power setting unit 905 sets a transmission powervalue corresponding to a distance between a transmission antenna element(may be hereinafter referred to as a “transmission antenna”) and areception antenna element (may be hereinafter referred to as a“reception antenna”) as necessary to achieve accuracy of a correctionvalue through predetermined calibration. The first transmission powersetting unit 905 gives the first transmission correction processing unit9061 the set transmission power value.

The first transmission correction processing unit 9061 gives the firstmodulating unit 907 a signal to be transmitted, while maintaining acorrection value with the phase and the amplitude that are currentlyset. The first modulating unit 907 performs modulation such as OFDM onthe signal given from the first transmission correction processing unit9061. The first modulating unit 907 gives the first switching unit 908the modulated signal.

The first switching unit 908 switches between transmission and receptionof the TDD. The first switching unit 908 passes, to the first antennaelement 909, the modulated signal given from the first modulating unit907. The first antenna element 909 transmits the modulated signal givenfrom the first modulating unit 907.

The second antenna elements 922 to the n-th antenna element 935 receivethe signal transmitted by the first antenna element 909. Here, incontrast to the first switching unit 908, the second switching unit 921to the n-th switching unit 934 make connections to enable reception ofsignals by the second reception system to the n-th reception system,respectively.

The second demodulating unit 923 to the n-th demodulating unit 936demodulate the signals received by the second antenna elements 922 tothe n-th antenna element 935, respectively, to, for example, OFDM. Thesecond reception correction processing unit 9251 to the n-th receptioncorrection processing unit 9381 are given the signals demodulated by thesecond demodulating unit 923 to the n-th demodulating unit 936,respectively.

The second reception correction processing unit 9251 to the n-threception correction processing unit 9381 give a demodulated signalgiven from the second demodulating unit 923 to the n-th demodulatingunit 936 to the second calibration RS extracting unit 926 to the n-thcalibration RS extracting unit 939, respectively, while maintainingphases and amplitudes that are currently set.

The second calibration RS extracting unit 926 to the n-th calibration RSextracting unit 939 extract cal-RS portions from the signal given fromthe second reception correction processing unit 9251 to the n-threception correction processing unit 9381 and give them to the secondresponse characteristics calculating unit 927 to the n-th responsecharacteristics calculating unit 940, respectively.

Based on a fact that the transmitted cal-RSs are known, the secondresponse characteristics calculating unit 927 to the n-th responsecharacteristics calculating unit 940 calculate propagation propertiesfrom fluctuations in the known signals. The second responsecharacteristics calculating unit 927 to the n-th responsecharacteristics calculating unit 940 notify the control unit 9411 of thecalculated propagation properties.

The control unit 9411 calculates a correction value, for example, withrespect to the second antenna element 922 so that the phases and theamplitudes are identical to the phase and the amplitude of the secondantenna element 922. Here, the correction value is calculated inconsideration of the respective distances of the second antenna element922 to the n-th antenna element 935 from the first antenna element 909.

Upon setting the calculated correction value to each of the secondreception correction processing unit 9251 to the n-th receptioncorrection processing unit 9381, the control unit 9411 can match thephases and the amplitudes of signals received by the second antennaelement 922 to the n-th antenna element 935.

If the first and third reception systems are calibrated with the sameprocesses with transmission from the second transmission system, thecorrection value for the first reception correction processing unit 9121can also be calculated. Thus, the phase and the amplitude of the firstreception system can be matched with those of the second receptionsystem.

Although the above examples describe reception of the same averagereception power through all the antenna elements, they are not limitedto such. Side lobes may be reduced by, for example, tapering the antennaelements to change the average reception power for each of the antennaelements. Here, the amplitude value of a received signal can be changedto a desired value by comparing the amplitude value with a desiredamplitude value in a normal operation, for example, before shipment.

FIGS. 11 and 12 are block diagrams illustrating an example configurationof the PHY processing unit 901, the control unit 9411, and the n antennaelements 909, 922, . . . , and 935. FIGS. 11 and 12 are connected acrossa border BL2. Since the configuration of FIGS. 11 and 12 is the same asthat of FIGS. 9 and 10, the same references will be assigned to the sameportions and the common description thereof will be omitted.

Following the calibration of the reception systems illustrated in FIGS.9 and 10, FIGS. 11 and 12 illustrate an example calibration oftransmission systems using the relative calibration in the TDD systems,with the same configuration as that in FIGS. 9 and 10.

When the control unit 9411 determines to execute calibration, the PHYprocessing unit 901 performs the following processes according to aninstruction from the control unit 9411.

The first transmission data generating unit 903 generates transmissiondata, and gives it to the first calibration RS mapping unit 904. Thefirst calibration RS mapping unit 904 maps (inserts) cal-RSs to betransmitted with the timing and at the frequency that are instructed bythe control unit 9411, to the transmission data given from the firsttransmission data generating unit 903. The first calibration RS mappingunit 904 gives the first transmission power setting unit 905 thetransmission data to which the cal-RSs are mapped.

The first transmission power setting unit 905 sets a transmission powervalue corresponding to a distance between a transmission antenna and areception antenna as necessary to achieve accuracy of a correction valuethrough predetermined calibration. The first transmission power settingunit 905 gives the first transmission correction processing unit 9061the set transmission power value.

The first transmission correction processing unit 9061 gives the firstmodulating unit 907 a signal to be transmitted, while maintaining acorrection value with the phase and the amplitude that are currentlyset. The first modulating unit 907 performs modulation such as OFDM onthe signal given from the first transmission correction processing unit9061. The first modulating unit 907 gives the first switching unit 908the modulated signal.

The first switching unit 908 switches between transmission and receptionof the TDD. The first switching unit 908 passes, to the first antennaelement 909, the modulated signal given from the first modulating unit907. The first antenna element 909 transmits the modulated signal givenfrom the first modulating unit 907.

The described processes may be performed in an order of the secondtransmission system, the third transmission system, . . . , and the n-thtransmission system, or a part of the processes may be simultaneouslyperformed by a plurality of the transmission systems. Simultaneouslyperforming the part of the processes can shorten a time required forcalibration.

Furthermore, transmission systems for performing the processes may beadded one by one as in REV method, for example, the second transmissionsystem, the second transmission system+the third transmission system, .. . , and the second transmission system+the third transmission system+. . . +the n-th transmission system.

The second antenna elements 922 to the n-th antenna element 935 receivethe signal transmitted by the first antenna element 909. Here, incontrast to the first switching unit 908, the second switching unit 921to the n-th switching unit 934 make connections to enable reception ofsignals by the second reception system to the n-th reception system,respectively.

The second demodulating unit 923 to the n-th demodulating unit 936demodulate the signals received by the second antenna elements 922 tothe n-th antenna element 935, respectively, to, for example, OFDM. Thesecond reception correction processing unit 9251 to the n-th receptioncorrection processing unit 9381 are given the signals demodulated by thesecond demodulating unit 923 to the n-th demodulating unit 936,respectively.

The second reception correction processing unit 9251 to the n-threception correction processing unit 9381 give a demodulated signalgiven from the second demodulating unit 923 to the n-th demodulatingunit 936 to the second calibration RS extracting unit 926 to the n-thcalibration RS extracting unit 939, respectively, while maintainingphases and amplitudes that are currently set.

The second calibration RS extracting unit 926 to the n-th calibration RSextracting unit 939 extract cal-RS portions from the signal given fromthe second reception correction processing unit 9251 to the n-threception correction processing unit 9381 and give them to the secondresponse characteristics calculating unit 927 to the n-th responsecharacteristics calculating unit 940, respectively.

Based on a fact that the transmitted cal-RSs are known, the secondresponse characteristics calculating unit 927 to the n-th responsecharacteristics calculating unit 940 calculate propagation propertiesfrom fluctuations in the known signals. The second responsecharacteristics calculating unit 927 to the n-th responsecharacteristics calculating unit 940 notify the control unit 9411 of thecalculated propagation properties.

The control unit 9411 calculates a correction value so that, forexample, phases of the second to the n-th transmission signalstransmitted through the second antenna element 922 to the n-th antennaelement 935, respectively, are identical to one another with respect tothe reception system including the first antenna element 909. Here, thecorrection value is calculated in consideration of the respectivedistances (phase rotation by a distance, amplitude attenuation) amongthe first antenna element 909 to the n-th antenna element 935.

Upon adding the calculated correction value to the current correctionvalue and setting the correction value to each of the secondtransmission correction processing unit 9191 to the n-th transmissioncorrection processing unit 9321, the control unit 9411 can match thephases and the amplitudes of signals transmitted by the second antennaelement 922 to the n-th antenna element 935.

If the second reception system is calibrated with the same processeswith transmission from the first transmission system, the phase and theamplitude of the first transmission system can be also matched with theothers.

Although the above examples describe transmission of the same averagetransmission power through all the antenna elements, they are notlimited to such. Side lobes may be reduced by, for example, tapering theantenna elements to change the average transmission power for each ofthe antenna elements. Here, the amplitude value of a transmission signalcan be changed to a desired value by comparing the amplitude value witha desired amplitude value that is known.

FIGS. 13 and 14 are block diagrams illustrating another exampleconfiguration of a PHY processing unit 901A, a control unit 9412, andthe n antenna elements 909, 922, . . . , and 935. FIGS. 13 and 14 areconnected across a border BL3.

The PHY processing unit 901A includes a plurality of encoder units, aplurality of modulating units, a plurality of switching units, aplurality of demodulating units, a plurality of decoder units. The PHYprocessing unit 901A corresponds to a calibration unit.

The plurality of encoder units are n encoder units (n is a naturalnumber) consisting of, specifically, a first encoder unit 902A, a secondencoder unit 915A, . . . , and an n-th encoder unit 928A. The pluralityof modulating units are n modulating units (n is a natural number)consisting of, specifically, the first modulating unit 907, the secondmodulating unit 920, . . . , and the n-th modulating unit 933. Theplurality of switching units are n switching units (n is a naturalnumber) consisting of, specifically, the first switching unit 908, thesecond switching unit 921, . . . , and the n-th switching unit 934.

The plurality of demodulating units are n demodulating units (n is anatural number) consisting of, specifically, the first demodulating unit910, the second demodulating unit 923, . . . , and the n-th demodulatingunit 936. The plurality of decoder units are n decoder units (n is anatural number) consisting of, specifically, a first decoder unit 911A,a second decoder unit 924A, . . . , and an n-th decoder unit 937A.

Furthermore, a plurality of antenna elements, specifically, the nantenna elements (n is a natural number) consisting of the first antennaelement 909, the second antenna element 922, . . . , and the n-thantenna element 935 are provided to correspond to the plurality ofencoder units 902A, 915A, . . . , and 928A, and the plurality of decoderunits 911A, 924A, . . . , and 937A, respectively.

The first encoder unit 902A includes the first transmission datagenerating unit 903, the first calibration RS mapping unit 904, thefirst transmission power setting unit 905, and a first transmissionphase rotation unit 9062. The first decoder unit 911A includes a firstreception phase rotation unit 9122, the first calibration RS extractingunit 913, and the first response characteristics calculating unit 914.

The second encoder unit 915A includes the second transmission datagenerating unit 916, the second calibration RS mapping unit 917, thesecond transmission power setting unit 918, and a second transmissionphase rotation unit 9192. The second decoder unit 924A includes a secondreception phase rotation unit 9252, the second calibration RS extractingunit 926, and the second response characteristics calculating unit 927.

The n-th encoder unit 928A includes the n-th transmission datagenerating unit 929, the n-th calibration RS mapping unit 930, the n-thtransmission power setting unit 931, and an n-th transmission phaserotation unit 9322. The n-th decoder unit 937A includes an n-threception phase rotation unit 9382, the n-th calibration RS extractingunit 939, and the n-th response characteristics calculating unit 940.

In FIGS. 13 and 14, the first encoder unit 902A, the first modulatingunit 907, the first switching unit 908, and the first antenna element909 form a first transmission system. The second encoder unit 915A, thesecond modulating unit 920, the second switching unit 921, and thesecond antenna element 922 form a second transmission system. The n-thencoder unit 928A, the n-th modulating unit 933, the n-th switching unit934, and the n-th antenna element 935 form an n-th transmission system.

In FIGS. 13 and 14, the first antenna element 909, the first switchingunit 908, the first demodulating unit 910, and the first decoder unit911A form a first reception system. The second antenna element 922, thesecond switching unit 921, the second demodulating unit 923, and thesecond decoder unit 924A form a second reception system. The n-thantenna element 935, the n-th switching unit 934, the n-th demodulatingunit 936, and the n-th decoder unit 937A form an n-th reception system.

Since the configuration of FIGS. 13 and 14 includes the sameconfiguration as that of FIGS. 9 and 10, the same references will beassigned to the same portions and the common description thereof will beomitted. FIGS. 13 and 14 illustrate an example of the REV method in theTDD systems. FIGS. 13 and 14 illustrate an example in which the secondreception phase rotation unit 9252 to the n-th reception phase rotationunit 9382 successively rotate the phases and the control unit 9412obtains a phase having the highest reception power, while the firsttransmission system makes a transmission and the second to the n-threception systems receive the transmission.

FIGS. 15 and 16 are block diagrams illustrating another exampleconfiguration of the PHY processing unit 901A, the control unit 9412,and the n antenna elements 909, 922, . . . , and 935. FIGS. 15 and 16are connected across a border BL4. Since the configuration of FIGS. 15and 16 is the same as that of FIGS. 13 and 14, the same references willbe assigned to the same portions and the common description thereof willbe omitted.

Following the calibration of the reception systems illustrated in FIGS.13 and 14, FIGS. 15 and 16 illustrate an example calibration oftransmission systems in the REV method using the TDD systems, with thesame configuration as that in FIGS. 13 and 14. FIGS. 15 and 16illustrate an example in which the second transmission phase rotationunit 9192 to the n-th transmission phase rotation unit 9322 successivelyrotate the phases, and the control unit 9412 obtains a phase having thehighest reception power.

When each of the calibration RS mapping units 904 to 930 transmits thecal-RSs, it may radio-transmit an information bit indicating that thesubframe or the slot is used for calibration so that a user equipment,the surrounding repeaters, and the surrounding cells can recognize thecalibration.

The user equipment can perform random access by avoiding the timing ofcalibration (may be hereinafter referred to as “calibration timing”).The surrounding repeaters and the surrounding cells can avoidsimultaneous calibration. Alternatively, the surrounding repeaters andthe surrounding cells may be notified through a cable. Alternatively,the surrounding user equipments may be notified via the surroundingrepeaters and the surrounding cells through a cable.

Notification of whether calibration is normally performed is effective.If the calibration is not normally performed, it is probable that, forexample, some antenna elements are electrically or physically damagedand lack their function. Thus, having a function of detecting, no matterhow many times a correction value is measured, whether the correctionvalue is significantly larger than values set in the past (including avalue set immediately before) is also effective.

If a failure in calibration is detected, for example, the reciprocity oftransmission and reception cannot be guaranteed. Thus, theprecoding/postcoding under control of beams may not operate normally,and the SNR becomes worse. Accordingly, communication cannot beperformed normally, and interference occurs in a cell that is normallyoperating.

Thus, notifying an RRC IDLE user equipment existing in the area that thecalibration is not normally performed, through broadcast information iseffective. Furthermore, individually notifying a user equipment duringcommunication using the radio resource control (RRC) is effective.Furthermore, notifying a user equipment moving into a cell throughhandover as configuration information for the cell is effective.

There are the following five calibration states (1) to (5).

(1) State 1: Calibration has not yet been executed.

(2) State 2: During calibration

(3) State 3: Calibration has failed.

(4) State 4: Calibration is to be started after a predetermined time.

(5) State 5: Calibration has been normally completed.

Notifying information indicating each of the above five calibrationstates (1) to (5) separately from information indicating whethercalibration is successful is effective.

Alternatively, collectively notifying some of the states (1) to (5)enables an amount of information to be reduced, which is effective.

Notifying a calibration level, specifically, information indicating, forexample, whether the reciprocity can be supported and whether adirection of arrival can be ascertained is also effective. Notifyingthis information to an RRC IDLE user equipment existing in the areathrough broadcast information is effective. Furthermore, individuallynotifying a user equipment during communication of such informationusing an RRC message such as an RRC connection setup message and an RRCconnection reconfiguration message is effective. Furthermore, notifyingalso a user equipment moving into a cell through handover of suchinformation as configuration information for the cell is effective.

Similarly, individually notifying, using the radio resource control(RRC), a base station about whether a user equipment is normallyperforming calibration or about a calibration state is effective.

As described above according to the first embodiment, the PHY processingunit that is a calibration unit obtains a correction value for thephases and the amplitudes of the beams in the respective antennaelements so that the phases and the amplitudes of the beams areidentical among the antenna elements, and calibrates the phases and theamplitudes based on the obtained correction value. Since the calibrationcan be performed with higher accuracy, it is possible to match phase andamplitude differences in beam among a plurality of antenna elementsincluded in a multi-element antenna. Thus, a communication systemcapable of communication with a relatively high throughput can beimplemented.

Second Embodiment

The first embodiment describes a method for enabling improvement of athroughput by matching phase and amplitude differences among antennaelements included in a multi-element antenna. The second embodiment willdisclose a method for solving a problem with requiring a long time totransmit the same number of cal-RSs when mapping of the cal-RSs for eachof the antenna elements for calibration temporally varies.

This method is a method for arranging reference signals for calibration(cal-RSs) in the same subframe in an antenna element that transmits thecal-RSs.

FIG. 17 illustrates example mapping in transmission data of a firstantenna element. FIG. 18 illustrates example mapping in transmissiondata of a second antenna element to an n-th antenna element. Thehorizontal axis represents a time t, and the vertical axis represents afrequency f in FIGS. 17 and 18. In FIGS. 17 and 18, a reference “1306”denotes a resource block.

In the example of FIG. 17, the first antenna element transmits cal-RSs1302 that are localized in a first slot 1303 and a first subframe 1304,and transmits normal OFDM symbols 1301 in the remaining portions.

As illustrated in FIG. 18, transmission data during the same duration inthe second antenna element to the n-th antenna element is a null 1307.In other words, in the second antenna element to the n-th antennaelement, the transmission data in a slot 1308 and a subframe 1309 duringa duration in which the cal-RSs 1302 are to be transmitted by the firstantenna element is the null 1307, whereas normal OFDM symbols 1305 aretransmitted in the remaining portions.

Although the slot indicates a time corresponding to 7 OFDM symbols andthe subframe indicates a time corresponding to 14 OFDM symbols, they maybe any minimum slot allocated on a per particular user unit basis.

Since the cal-RSs 1302 are arranged during a particular duration in theexample of FIG. 17, calibration is possible during this duration and thetime required for calibration can be shortened.

Although the first antenna element transmits the cal-RSs 1302 with thesecond and third OFDM symbols in the example of FIG. 17, transmittingcal-RSs of another antenna element using the fourth and fifth OFDMsymbols in the same slot or the same subframe is also effective.

Furthermore, not only shifting the time but also using a differentorthogonal code is effective to enable the cal-RSs for each of theantenna elements to be orthogonalized and separated. It is morepreferred to set a code to an orthogonal code even with the phaserotated.

Similarly, transmitting the cal-RSs at a part of the frequencies throughthe first antenna element and transmitting the cal-RSs at a differentfrequency through another antenna element are also effective.

The cal-RSs may be identical signals among all the antenna elements ifcode-multiplexing is not used.

Since such processes enable use of the energy in the entire frequencydomain, the SNR can be increased and the accuracy of calibration can beimproved. Furthermore, since nothing is transmitted through the otherantenna elements, interference can be reduced and the accuracy ofcalibration can be improved.

The method for transmitting the cal-RSs in a particular frequency domainis effective when the SNR is sufficiently favorable. Since a pluralityof antenna elements can be simultaneously calibrated using this method,the time required for calibration can be shortened.

In the REV method, the same signals as those of the first antennaelement may be mapped for the second to the n-th antenna elements,instead of the null.

FIG. 19 illustrates examples of mapping and the reception power at eachfrequency, in transmission data of the first antenna element. Part (a)of FIG. 19 illustrates an example of mapping in the transmission data ofthe first antenna element, and part (b) of FIG. 19 illustrates thereception power at each frequency in the transmission data of the firstantenna element.

In the example of FIG. 19, the first antenna element transmits cal-RSs1402 that are localized in a first slot 1403 and a first subframe 1404,and transmits normal OFDM symbols 1401 in the remaining portions,similarly as the example in FIG. 17.

Since the entire frequency domain is used herein, responsecharacteristics at each frequency can be calculated. Thus, fluctuationsin the amplitude and the phase at each frequency can be detected.Fluctuations in the received power are calculated from the detectedamplitude and phase. As illustrated in FIG. 19, when fluctuations in thereceived power P for each of the OFDM symbols 1401 are larger, it ispossible to determine the presence of frequency-selective multipathfading.

When transmission antenna elements and reception antenna elements forcalibration are not moved and the multipath is detected, it is possibleto determine occurrence of a state different from a normal state such asthe presence of scatterers in close proximity. No calibration at thesub-band is effective. Here, it is preferred to use the correction valuein the previous calibration and the phase rotation.

Since the scatterers occurring in close proximity normally move far in apredetermined time, detecting fluctuations in the amplitude and thephase at each frequency again after a lapse of a certain time iseffective.

Alternatively, the fluctuations may be calculated and set from thecorrection value and the phase rotation at the close band. Interpolationsuch as linear interpolation is also effective.

Furthermore, when the multipath is detected, separation betweenprincipal waves and delay waves through, for example, calculation of adelay profile and calibration only with the principal waves areeffective. Accordingly, influence of the multipath can be removed, andappropriate calibration can be performed.

According to the second embodiment, when transmitting respective cal-RSsfrom a plurality of antenna elements, the PHY processing unit that is acalibration unit arranges the cal-RSs in the same subframe as describedabove. Accordingly, since all the antenna elements can be calibratedduring the same duration, the time required for calibration can beshortened.

Third Embodiment

The second embodiment describes a method for temporally localizing themapping of cal-RSs for each antenna element that is required forcalibration to enable shortening of the time required for calibration.However, the transmission sometimes overlaps with those of the other CHsor the other RSs, and the current standards do not cover suchrequirement. Thus, a non-avoidable problem with the requirement occurs.The third embodiment will disclose a method for solving the problem byproviding a new mapping method.

FIG. 20 illustrates another example mapping in the transmission data ofthe first antenna element. FIG. 21 illustrates another example mappingin the transmission data of the second antenna element to the n-thantenna element. FIGS. 20 and 21 illustrate example mapping of downlinktransmission bits for which a slot or a subframe for calibration orresource blocks 1504 and 1508 are provided.

As illustrated in FIG. 20, special mapping of not transmitting a part ofCRSs 1503 on a subframe for transmitting cal-RSs 1502 is provided forthe first antenna element. Normal OFDM symbols 1501 are transmitted inthe remaining portions.

As illustrated in FIG. 21, special mapping of not transmitting a part ofCRSs 1507 on a subframe for transmitting a null 1506 is provided for thesecond antenna element to the n-th antenna element. Normal OFDM symbols1505 are transmitted in the remaining portions.

FIG. 22 further illustrates another example mapping in the transmissiondata of the first antenna element. FIG. 23 further illustrates anotherexample mapping in the transmission data of the second antenna element.FIG. 24 further illustrates another example mapping in the transmissiondata of the third antenna element. FIG. 25 further illustrates anotherexample mapping in the transmission data of the fourth antenna element.

In FIGS. 22, 23, 24, and 25, references “1604”, “1608”, “1612”, and“1616” denote resource blocks, and references “1601”, “1605”, “1609”,and “1613” denote normal OFDM symbols, respectively.

As illustrated in FIGS. 22, 23, 24, and 25, possible positions ofcal-RSs 1602, 1606, 1610, and 1614 may be defined in advance only withthe timing that does not overlap CRSs 1603, 1607, 1611, and 1615,respectively. Here, the cal-RSs can be arranged, for example, onlybetween the first OFDM symbol and the third OFDM symbol or between thefourth OFDM symbol and the fifth OFDM symbol in each slot.

FIG. 26 further illustrates another example mapping of transmission datain the transmission data of the first antenna element. FIG. 27 furtherillustrates another example mapping in transmission data of the secondantenna element to the n-th antenna element. In FIGS. 26 and 27,references “1704” and “1708” denote resource blocks, and references“1701” and “1705” denote normal OFDM symbols, respectively. Furthermore,in FIG. 27, a reference “1706” denotes a null.

As illustrated in FIGS. 26 and 27, cal-RSs 1702 may be mapped topositions that do not overlap mapping positions of CRSs 1703 and 1707,respectively. With this, a collision can be avoided.

Alternatively, as illustrated in FIGS. 20 and 21, when cal-RSs overlapthe other CHs or the other RSs, the cal-RSs may be preferentiallyarranged.

As described above, the PHY processing unit that is a calibration unitarranges the cal-RSs in positions where the other reference signals orthe other physical channels of a subframe are not arranged according tothe third embodiment. Accordingly, since the timing of transmitting thecal-RSs can be prevented from overlapping the timing of transmitting theother reference signals or the other physical channels, the cal-RSs canavoid a collision with the other reference signals or the other physicalchannels.

Fourth Embodiment

The third embodiment discloses providing a subframe for calibration andtransmitting RSs for calibration (cal-RSs) on the subframe. A basestation may not transmit the other channels (abbreviated as CHs) or theother RSs on the subframe. The subframe for calibration of nottransmitting the other CHs or the other RSs will be referred to as acalibration-specific subframe.

However, the base station normally transmits some physical CHs or RSsthat are not intended for calibration, every subframe. Thus, without anyingenuity, a problem with incapability to configure acalibration-specific subframe occurs. The fourth embodiment willdisclose a method for solving such a problem.

A base station sets a subframe having no data to be transmitted to acalibration-specific subframe. The base station may set a subframehaving no data to be scheduled to a calibration-specific subframe. Thebase station sets one or more subframes included in subframes having nodata to be transmitted or scheduled to calibration-specific subframes.The one or more subframes may be determined according to the necessityof the calibration-specific subframes.

The base station determines a radio link at which thecalibration-specific subframe is set. For example, when there is no datato be scheduled in a DL subframe, the DL subframe is set to acalibration-specific subframe. Alternatively, when there is no data tobe scheduled in a UL subframe, the UL subframe may be set to acalibration-specific subframe. Alternatively, when there is no data tobe scheduled in either a DL subframe or a UL subframe with the sametiming as the DL subframe, at least one of the DL subframe and the ULsubframe may be set to a calibration-specific subframe.

The base station may determine in advance a radio link to be calibrated.The radio link is determined in advance as, for example, the DL. Here,when there is no data to be scheduled in a DL subframe, the DL subframeis set to a calibration-specific subframe. Thus, even when there is nodata to be scheduled in a UL subframe, the UL subframe is not set to acalibration-specific subframe. Here, the UL is not used for setting acalibration-specific subframe.

When a radio link to be calibrated is set to the DL, it is possible toeliminate influence of interference with the UL from a UE. For example,when a base station that supports the TDD sets a radio link to becalibrated to the DL, it can execute calibration without influence ofinterference caused by uplink transmission performed by a UE beingserved by a cell having an antenna to be calibrated and by a UE beingserved by another cell or another base station. Examples of the uplinktransmission in the LTE include a SR and a PRACH. As such, using the DLin calibration can further improve the accuracy of calibration.

As an alternative example, a base station that supports the FDD setsradio links to be calibrated to the DL and the UL. When there is no datato be scheduled in either a DL subframe or a UL subframe with the sametiming as the DL subframe, both of the DL subframe and the UL subframeare set to calibration-specific subframes. Accordingly, calibration fora transmission system and a reception system of an antenna element canbe performed within these subframes, and the time required forcalibration can be shortened.

The base station detects a subframe having no data to be transmitted orscheduled, and sets the subframe to a calibration-specific subframe.

The following four examples (1) to (4) will be disclosed as examplesubjects that detect a subframe having no data to be transmitted orscheduled.

(1) Scheduler

This option may be used when, for example, a scheduler performsscheduling. It is easy to provide the scheduler with a function ofdetecting the presence or absence of data to be transmitted orscheduled.

(2) MAC

This option may be used when, for example, the MAC performs scheduling.It is easy to provide the MAC with the function of detecting thepresence or absence of data to be transmitted or scheduled.

(3) PHY Processing Unit

This option may be used when, for example, a subframe having no data tobe transmitted is detected. It is easy to provide the PHY processingunit with a function of detecting the presence or absence of data to betransmitted.

(4) RRC

This option may be used when, for example, the RRC sets the DRX, etc.The RRC recognizes, through the DRX, a subframe on which data is nottransmitted or scheduled. Thus, it is easy to provide the RRC with thefunction of detecting the presence or absence of data to be transmittedor scheduled.

The following four examples (1) to (4) will be disclosed as examplesubjects that set the detected subframe to a calibration-specificsubframe.

(1) Scheduler

This option may be used when, for example, a scheduler, the MAC, or theRRC detects the presence or absence of data to be transmitted orscheduled. When the scheduler, the MAC, or the RRC detects the absenceof the data, the scheduler is notified of the absence of the data. Thescheduler sets the subframe detected using the information to acalibration-specific subframe.

(2) MAC

The scheduler described in (1) above may be replaced with the MAC.

(3) PHY Processing Unit

This option may be used when, for example, the scheduler, the MAC, thePHY processing unit, or the RRC detects the presence or absence of datato be transmitted or scheduled. When the scheduler, the MAC, the PHYprocessing unit, or the RRC detects the absence of the data, the PHYprocessing unit is notified of the absence of the data. The PHYprocessing unit sets the subframe detected using the information to acalibration-specific subframe.

(4) RRC

This option may be used when, for example, the RRC detects the presenceor absence of data to be transmitted or scheduled. When the RRC detectsthe absence of the data, it sets the subframe detected using theinformation to a calibration-specific subframe.

Aside from these, the subjects that detect a subframe having no data tobe transmitted or scheduled and the subjects that set a subframe to acalibration-specific subframe may be appropriately combined. Thesubjects may be combined according to a configuration of a base stationand the required performance.

The base station determines which antenna element is to be calibrated.The base station determines which antenna element is categorized as atransmission antenna element for calibration or as a reception antennaelement for calibration.

The base station maps RSs for calibration (cal-RSs) of the transmissionantenna element for calibration to a calibration-specific subframe.Cal-RSs of a plurality of antenna elements may be mapped to onecalibration-specific subframe. The PHY processing unit may map thecal-RSs using information on a calibration-specific subframe.

The subject that sets a calibration-specific subframe may notify the PHYprocessing unit of the information on the calibration-specific subframe.The base station transmits cal-RSs of a transmission antenna forcalibration on the calibration-specific subframe.

The RSs for calibration may not be specific to calibration. The RSs maybe used for other applications. Alternatively, the existing RSs may beused instead. Examples of the existing RSs include CRSs, CSI-RSs, andsounding reference signals (SRS), etc. Which RSs are to be used may bedetermined in advance, and the RSs may be mapped to acalibration-specific subframe. A sequence or a resource to be mapped hasalready been determined for the existing RSs. Since no new RS is set,the complexity of a communication system can be avoided.

Furthermore, the calibration-specific subframes may be used for otherapplications. The RSs to be used for other applications may be mapped toa calibration-specific subframe. The method disclosed in the fourthembodiment is applicable.

A base station that transmits cal-RSs from a transmission antennaelement for calibration on a calibration-specific subframe receives thecal-RSs on the calibration-specific subframe through a reception antennaelement for calibration. The base station derives a calibration valuefor a transmission system of an antenna element, using a receptionresult of the cal-RSs for each transmission antenna element forcalibration.

The base station may calibrate a reception system of an antenna elementin a similar method. The base station that transmits cal-RSs from atransmission antenna element for calibration on a calibration-specificsubframe receives the cal-RSs on the calibration-specific subframethrough a reception antenna element for calibration. The base stationderives a calibration value for the reception system of the antennaelement, using a reception result of the cal-RSs for each receptionantenna element for calibration.

FIG. 28 is a flowchart indicating an example procedure on calibrationprocesses in the communication system according to the fourthembodiment. FIG. 28 illustrates an example self-calibration in a basestation.

In Step ST4101, the base station determines to execute calibration. Thejudgment indicators disclosed in the first embodiment may be used inthis determination.

In Step ST4102, the base station determines the presence or absence of asubframe having no data to be transmitted (may be hereinafter referredto as “non-transmission-data subframe”). This determination may be made,for example, per subframe. This determination may be made per aplurality of subframes. When the presence of a non-transmission-datasubframe is determined, the processes proceed to Step ST4103. When theabsence of the non-transmission-data subframe is determined, theprocesses will be put on hold until the presence of thenon-transmission-data subframe is determined.

In Step ST4103, the base station sets the subframe detected in StepST4102 to a calibration-specific subframe.

In Step ST4104, the base station maps RSs for calibration (cal-RSs) of atransmission antenna element for calibration to the calibration-specificsubframe. Here, the base station may determine which antenna element iscategorized as a transmission antenna element for calibration or as areception antenna element for calibration. More specifically, in StepST4104, the base station transmits the cal-RSs of the transmissionantenna for calibration on the calibration-specific subframe.

In Step ST4105, the base station receives the cal-RSs on thecalibration-specific subframe through a reception antenna element forcalibration.

In Step ST4106, the base station derives a calibration value for atransmission system of an antenna element, using a reception result ofthe cal-RSs for each transmission antenna element for calibration.

In Step ST4107, the base station determines whether calibration on allthe antenna elements is completed. When the completion of thecalibration on all the antenna elements is determined, the processesproceed to Step ST4108. If it is determined that the calibration on allthe antenna elements has not been completed, the processes return toStep ST4102 to perform the aforementioned processes on an antennaelement that has not been calibrated. The processes may be performeduntil completion of the calibration of transmission systems andreception systems of all the antenna elements.

In Step ST4108, the processes return to a normal operation. In thenormal operation, the calibration ends, and a normal communicationservice is provided to user equipments being served. The entireprocedure ends after the process in Step ST4108.

Using the method disclosed in the fourth embodiment, a base station canbe equipped with a subframe for calibrating a multi-element antenna.Accordingly, the base station can calibrate antenna elements. Thus, theperformance of the MIMO and the beamforming using the multi-elementantenna can be improved.

The fourth embodiment discloses that a base station sets a subframehaving no data to be transmitted or scheduled to a calibration-specificsubframe. As an alternative method, the subframe having no data to betransmitted or scheduled may be replaced with a subframe whose data tobe transmitted or scheduled is smaller than or equal to a predeterminedamount of data. With a small amount of data, calibration can bepreferentially executed.

The predetermined amount of data may be determined in advance or setaccording to an operational environment and an operational state. Thepredetermined amount of data is set, for example, according to anambient temperature. Alternatively, the predetermined amount of data isset, for example, according to a load of a base station. When thesubframe has data smaller than or equal to the predetermined amount ofdata, it means that the subframe has data to be transmitted orscheduled. A method, which will be disclosed in the second modificationof the fourth embodiment, for storing data not to be transmitted andtransmitting the data stored with the timing capable of subsequenttransmission of data may be applied to handling of this transmissiondata.

Accordingly, calibration can be executed flexibly according to theoperational environment. Thus, the performance of the MIMO and thebeamforming using the multi-element antenna can be improved.

According to the fourth embodiment, the PHY processing unit that is acalibration unit sets a subframe having no data to be transmitted orscheduled to a cal-specific subframe that is a subframe in which cal-RSsare arranged. Accordingly, even in the presence of data to betransmitted or scheduled, the cal-specific subframe can be configured.Thus, the calibration with higher accuracy can be performed as describedabove.

First Modification of the Fourth Embodiment

The fourth embodiment discloses setting a subframe having no data to betransmitted or scheduled to a calibration-specific subframe. However,some systems may have a subframe to which a signal and a CH to betransmitted irrespective of transmission data are mapped.

Examples of the signal and the CH to be transmitted irrespective oftransmission data include a synchronization signal required for initialsearch by a UE, a broadcast-information transmission CH, and a controlCH, etc. Examples of the signal and the CH in the LTE include an SS, aPBCH, and a PDCCH.

In the presence of the signal and the CH, a problem with incapability toconfigure a calibration-specific subframe even according to the methodof the fourth embodiment occurs. The first modification will disclose amethod for solving this problem.

The base station sets a subframe to which the signal and the CH to betransmitted irrespective of transmission data are not mapped, to acalibration-specific subframe. The base station sets one or moresubframes included in subframes to which the signal and the CH to betransmitted irrespective of transmission data are not mapped, tocalibration-specific subframes. The one or more subframes may bedetermined according to the necessity of the calibration-specificsubframes.

Among the signals and the CHs to be transmitted irrespective oftransmission data, this method may be applied to, for example, a signaland a CH for which the subframe where they are scheduled is determinedin advance, and a signal and a CH to be periodically or intermittentlyscheduled. These signals and CHs in the LTE include an SS and a PBCH.The subframe to which these signals and CHs are not mapped may be set toa calibration-specific subframe.

Another method will be disclosed. In the presence of a subframe havingno data to be transmitted or scheduled, a base station does nottransmit, on the subframe, the signal and the CH to be transmittedirrespective of transmission data. Among the signals and the CHs to betransmitted irrespective of transmission data, this method may beapplied to a signal and a CH for which the subframe where they arescheduled is not determined in advance, or a signal and a CH to betransmitted every subframe.

These signals and CHs in the LTE include a PDCCH, a PCFICH, and a CRS.The base station may not transmit, on one or more subframes included insubframes having no data to be transmitted or scheduled, the signal andthe CH to be transmitted irrespective of transmission data.

The base station sets a subframe on which the signal and the CH to betransmitted irrespective of transmission data are not transmitted, to acalibration-specific subframe. Furthermore, this method may be appliedto a signal and a CH for which the subframe where they are scheduled isdetermined in advance, and a signal and a CH to be periodically orintermittently scheduled. This method is applied to, for example, a casewhere calibration is required with timing having no transmission data,etc. Accordingly, the calibration timing can be optimized, and theaccuracy of calibration can be improved.

In the presence of a subframe having no data to be transmitted orscheduled, when the subframe is set to a calibration-specific subframe,the base station may not transmit, on the subframe, a signal and a CH tobe transmitted irrespective of transmission data. Accordingly, when thesubframe is not set to a calibration-specific subframe, the base stationcan transmit, on the subframe, a signal and a CH to be transmittedirrespective of transmission data, and maintain a normal operation.

The above two methods may be combined. Accordingly, the base station canset a calibration-specific subframe even in the presence of a signal anda CH for which the subframe where they are scheduled is determined inadvance, a signal and a CH to be periodically or intermittentlyscheduled, a signal and a CH for which the subframe where they arescheduled is not determined in advance, or a signal and a CH to betransmitted every subframe.

The methods according to the fourth embodiment may be applied to amethod for determining a radio link at which a calibration-specificsubframe is set, a method for detecting a subframe to which a signal anda CH to be transmitted irrespective of transmission data are not mapped,and a method for setting a calibration-specific subframe. Thetransmission data may be replaced with the signal and the CH to betransmitted irrespective of the transmission data.

FIG. 29 is a flowchart indicating an example procedure on calibrationprocesses in a communication system according to the first modificationof the fourth embodiment. FIG. 29 illustrates an exampleself-calibration in a base station. Since the flowchart of FIG. 29includes the same steps as those in the flowchart of FIG. 28 asdescribed above, the same step numbers will be assigned to the sameSteps and the common description thereof will be omitted.

After determining to execute calibration in Step ST4101, if the absenceof a non-transmission-data subframe is determined in Step ST4102, thebase station waits until the presence of the non-transmission-datasubframe is determined. If the presence of the non-transmission-datasubframe is determined in Step ST4102, the processes proceed to StepST4201.

In Step ST4201, the base station determines whether the SS and the PBCHare not transmitted on the subframe detected in Step ST4102. If it isdetermined that the SS and the PBCH are not transmitted on the detectedsubframe, the processes proceed to Step ST4103. If it is determined thatthe SS and the PBCH are transmitted on the detected subframe, theprocesses return to Step ST4102, and will be put on hold until thepresence of the non-transmission-data subframe is determined.

In Step ST4103, the base station sets the subframe detected in StepST4102 to a calibration-specific subframe. After the detected subframeis set to a calibration-specific subframe, the processes proceed to StepST4202.

In Step ST4202, the base station stops transmitting a PDCCH, a PCFICH,and a CRS on the calibration-specific subframe set in Step ST4103. Afterthe completion of the process in Step ST4202, the processes proceed toStep ST4104.

In Step ST4104, the base station maps RSs for calibration (cal-RSs) of atransmission antenna element for calibration to the calibration-specificsubframe. Here, the base station may determine which antenna element iscategorized as a transmission antenna element for calibration or as areception antenna element for calibration.

More specifically, in Step ST4104, the base station transmits thecal-RSs of the transmission antenna for calibration on thecalibration-specific subframe. After the completion of the process inStep ST4104, the processes in Step ST4105 to Step ST4108 will beperformed.

Even in the presence of a subframe to which a signal and a CH to betransmitted irrespective of transmission data are mapped, a subframe forcalibrating a multi-element antenna can be provided using the methoddisclosed in the first modification.

Accordingly, a subframe for calibration can be set more flexibly than bythe first embodiment. A calibration-specific subframe can be set withthe necessary timing such as when temperature variations suddenly becomelarger, etc.

Thus, since the base station can calibrate antenna elements with thenecessary timing, the performance of the MIMO and the beamforming usingthe multi-element antenna can be further improved.

According to the method above, in the presence of a subframe having nodata to be transmitted or scheduled, the base station does not transmit,on the subframe, a signal and a CH to be transmitted irrespective oftransmission data. However, the signal and the CH may be muted as analternative method. Furthermore, the transmission power may be zero.

In the presence of a subframe having no data to be transmitted orscheduled, the base station mutes, on the subframe, the signal and theCH to be transmitted irrespective of transmission data.

When the signal and the CH are not transmitted, the cal-RSs can bemapped to symbols to which the signal and the CH are to be mapped, thusenabling increase in the resource for cal-RSs.

In muting the signal and the CH, though the transmission power of thesignal and the CH is zero, the signal and the CH are mapped. Thus, theresource cannot be used for the cal-RSs. Although the resource forcal-RSs cannot be increased, only the adjustment to the transmissionpower is required. Thus, the configuration and the control for providinga calibration function can be facilitated.

According to the method above, in the presence of a subframe having nodata to be transmitted or scheduled, the base station either does nottransmit on the subframe or mutes a signal and a CH to be transmittedirrespective of transmission data. However, the following process may beperformed instead. Specifically, the base station may either nottransmit or mute the signal and the CH that overlap a resource fortransmitting cal-RSs.

As disclosed in the third embodiment, when cal-RSs overlap a signal anda CH to be transmitted irrespective of transmission data, the cal-RSsmay be preferentially mapped to the resource. Accordingly, when anamount of the resource required for the cal-RSs is smaller, the signaland the CH to be transmitted irrespective of transmission data can betransmitted, and decrease in communication performance when the signaland the CH are necessary can be prevented.

Second Modification of the Fourth Embodiment

In the fourth embodiment, a subframe having no transmission data is setto a calibration-specific subframe. However, there are some casesincluding a case where a base station has many UEs being served thereby,a case where a huge volume of data is communicated, and a case where thetiming of having no transmission data does not occur with the necessarytiming. Here, waiting for the timing of having no transmission datacauses problems with delay in the calibration and degradation in theperformance. The second modification will disclose a method for solvingsuch problems.

The base station controls the transmission timing of data to enable acalibration-specific subframe to be set with the necessary timing ofcalibration. The base station, for example, sets a calibration-specificsubframe with the necessary timing of calibration without transmittingdata. The base station stores data not to be transmitted, and transmitsthe stored data with the timing capable of subsequent transmission ofdata.

The base station detects the necessary timing of calibration. The timingmay be detected by, for example, the control unit 806 disclosedaccording to the first embodiment.

The base station may determine whether it is necessary to stoptransmitting data with the necessary timing of calibration. Thedetermination may be made, as a judgment criterion, depending on thepresence or absence of data to be transmitted with the timing. The basestation may determine that it is unnecessary to stop transmitting data,for example, in the absence of data to be transmitted with the timing.

The judging subject may be a subject that detects a subframe having nodata to be transmitted or scheduled as disclosed in the fourthembodiment. The subject is enabled to perform the judgment by obtaininginformation on the necessary timing of calibration from the control unit806.

When it is unnecessary to stop transmitting data, a calibration-specificsubframe is set with the timing. The method disclosed in the fourthembodiment may be applied thereto. When there is data to be transmittedwith the necessary timing of calibration, the base station stopstransmitting data, and sets a calibration-specific subframe.

The base station may determine the presence or absence of a signal and aCH to be transmitted irrespective of transmission data, with thenecessary timing of calibration. The method disclosed in the firstmodification of the fourth embodiment may be applied to thedetermination and the setting of a calibration-specific subframe.

The first modification of the fourth embodiment describes that, in thepresence of a signal and a CH for which the subframe where they arescheduled is determined in advance, and a signal and a CH to beperiodically or intermittently scheduled, a subframe to which thesesignals and CHs are not mapped may be set to a calibration-specificsubframe.

The necessary timing of calibration may or may not come within thesubframe to which these signals and CHs are not mapped. If not,transmission of these signals and CHs may be stopped and acalibration-specific subframe may be set.

The base station sets a calibration-specific subframe with the necessarytiming of calibration. Until completion of the calibration, the basestation does not transmit data. Transmission of the data may be held.

The base station sets a calibration-specific subframe during notransmission of data. A duration during no transmission of data may beset per subframe or at transmission time intervals (TTIs).

As an alternative method, data may not be transmitted during apredetermined duration including the set calibration-specific subframe.Setting the predetermined duration as short as possible can reduce adelay in transmitting data. Furthermore, it is possible to resumeearlier the transmission of a signal and a CH to be transmittedirrespective of transmission data and to minimize losses in thesynchronization and the control process in the UEs being served.

When the predetermined duration is set longer than thecalibration-specific subframe, detection of the necessary timing ofcalibration is deviated from the timing of transmitting data, and thusoccurrence of events such as a malfunction can be reduced. Thepredetermined duration may be statically predetermined, orsemi-statically or dynamically determined by a base station.

The base station stores data not to be transmitted, and transmits thestored data with the timing capable of subsequent transmission of data.The process of storing data not to be transmitted may be performed by,for example, a scheduler or the MAC. Furthermore, the process may beperformed by the PHY processing unit. The scheduler, the MAC, or the PHYprocessing unit may perform processes of storing, in an internal orexternal storage device, data not to be transmitted and of retrievingthe stored transmission data by the timing capable of subsequenttransmission of data.

The base station maps cal-RSs of a transmission antenna for calibrationto the set calibration-specific subframe, and transmits the cal-RSs onthe subframe. The base station performs calibration using thecalibration-specific subframe. The method disclosed in the fourthembodiment may be applied to this method.

The base station starts transmitting data with the timing capable oftransmission of data, after the predetermined duration. Furthermore, thebase station starts transmitting a signal and a CH to be transmittedirrespective of transmission data, after the predetermined duration.Accordingly, the base station returns to a normal operation.

FIG. 30 is a flowchart indicating an example procedure on calibrationprocesses in a communication system according to the second modificationof the fourth embodiment. FIG. 30 illustrates an exampleself-calibration in a base station. Since the flowchart of FIG. 30includes the same steps as those in the flowchart of FIG. 28 describedabove, the same step numbers will be assigned to the same Steps and thecommon description thereof will be omitted.

After determining to execute calibration in Step ST4101, the basestation determines whether the calibration timing has come in StepST4301. If the base station determines that the calibration timing hascome, the processes proceed to Step ST4302. If the base stationdetermines that the calibration timing has not come, the processes willbe put on hold until it is determined that the calibration timing hascome.

In Step ST4302, the base station determines the presence or absence oftransmission data. If the base station determines the presence oftransmission data, the processes proceed to Step ST4303. If the basestation determines the absence of transmission data, the processesproceed to Step ST4103.

In Step ST4303, the base station stops transmitting data with thecalibration timing, and stores the transmission data. After completionof the process in Step ST4303, the processes proceed to Step ST4103.

The base station that stores the transmission data in Step ST4303detects a non-transmission-data subframe with the calibration timing,and sets the detected subframe to a calibration-specific subframe inStep ST4103. After completion of the process in Step ST4103, theprocesses proceed to Step ST4104.

In Step ST4104, the base station maps cal-RSs of a transmission antennafor calibration to the set calibration-specific subframe, transmits thecal-RSs on the subframe, and performs calibration. Since this method isthe same as that in FIG. 28, the description thereof will be omitted.

After the processes in Steps ST4105 and ST4106, if it is determined inSteps ST4107 that calibration on all the antenna elements is completed,the processes proceed to Step ST4304. If it is determined that thecalibration on all the antenna elements has not been completed, theprocesses return to Step ST4302 to perform the aforementioned processeson an antenna element that has not been calibrated.

In Step ST4304, the base station resumes transmission of data includingthe stored data, with the timing capable of transmission of data.Accordingly, the base station returns to a normal operation. The entireprocedure ends after the process in Step ST4304.

Using the method disclosed in the second modification enables setting ofa calibration-specific subframe with the necessary timing ofcalibration, and execution of calibration on the subframe.

Accordingly, even when a base station has many UEs being served therebyor even when a huge volume of data is being communicated, it is possibleto prevent degradation in the performance caused by delay in thecalibration. Thus, the performance of the MIMO and the beamforming usingthe multi-element antenna can be further improved.

The method disclosed in the first modification of the fourth embodimentmay be applied to a case where there are a signal and a CH to betransmitted irrespective of transmission data with the necessary timingof calibration. Even in the presence of the signal and the CH to betransmitted irrespective of transmission data, a calibration-specificsubframe can be set with the necessary timing of calibration, andcalibration can be performed on the subframe.

Although what is disclosed in the aforementioned method is that the basestation stores data not to be transmitted and transmits the stored datawith the timing capable of subsequent transmission of data, the methodmay be the others. As an alternative method, the data not to betransmitted may be prevented from being stored and transmitted.Furthermore, the data not to be transmitted may be discarded withoutbeing stored.

For example, less important data may be prevented from being stored andtransmitted. Alternatively, transmission data with a smaller acceptableamount of delay may be prevented from being stored and transmitted.Examples of the data with a smaller acceptable amount of delay includeaudio data and real-time game data, etc. Furthermore, retransmissiondata may be prevented from being stored and transmitted. This is becausethe retransmission is performed and a problem is unlikely to occur evenif the retransmission data is skipped once or so. Accordingly, therequired storage capacity can be reduced.

Furthermore, the method according to the second modification of thefourth embodiment may be performed on the transmission data that can beheld. Furthermore, the method according to the fourth embodiment may beperformed on the transmission data that cannot be held.

Examples of the transmission data that can be held include data with alarger acceptable amount of delay. Alternatively, data with a lower QoSvalue or a larger QoS class identifier (QCI) value may be used. Examplesof the data include buffered streaming video data and File TransferProtocol (abbreviated as FTP) data, etc.

Examples of the transmission data that cannot be held include data witha smaller acceptable amount of delay. Alternatively, data with a higherQoS value or a smaller QCI value may be used. Such examples includeaudio data and real-time game data, etc.

Thus, the timing to execute calibration can be changed according to thetransmission data. Accordingly, the calibration during communication canbe more flexibly executed.

Although it is described that the method according to the secondmodification of the fourth embodiment is performed on the transmissiondata that can be held and the method according to the fourth embodimentis performed on the transmission data that cannot be held, the methodsare not limited to such. When the execution of calibration takespriority over transmission of data, the method according to the secondmodification of the fourth embodiment may be performed. Furthermore,when transmission of data takes priority over the execution ofcalibration, the method according to the fourth embodiment may beperformed. Similarly, the timing to execute calibration can be changedaccording to the transmission data. Accordingly, the calibration duringcommunication can be more flexibly executed.

According to the second modification, the PHY processing unit that is acalibration unit controls the timing to transmit data to enable asubframe in which the cal-RSs are arranged to be set. Accordingly, thecal-specific subframe can be set with the necessary timing ofcalibration. Consequently, it is possible to prevent delay in thecalibration and degradation in the performance caused by the delay inthe calibration.

Third Modification of the Fourth Embodiment

The third modification will disclose another method for solving theproblems described in the second modification of the fourth embodiment.The base station provides a subframe on which neither data nor a signalor a CH that are irrelevant to transmission data are transmitted. Thebase station provides a subframe on which nothing is transmitted. In thefollowing description, the subframe on which nothing is transmitted maybe referred to as a “complete blank subframe (CBS)”. The base stationmaps only RSs for calibration to a CBS.

The following (1) to (6) will be disclosed as example parameters forconfiguring the CBS.

(1) Offset; the offset represents the start timing. For example, atleast one of a start radio frame and a start subframe may be set.

(1) Duration; the duration is a duration during which the CBS occurs.For example, the number of one or more subframes may be set.

(3) Period; the period is a period with which the CBS occurs. This isuseful when the CBS is periodically caused to occur. For example, atleast one of the number of radio frames and the number of subframes maybe set.

(4) End timing; for example, at least one of an end radio frame and anend subframe may be set. As an alternative method, a duration from thestart to the end may be set. At least one of the number of radio framesand the number of subframes may be set. Furthermore, when the CBS is setto a long duration, for example, a year, a date, and a time may be set.Furthermore, the end timing may not be set. Here, once the CBS is set,the CBS is configured until a switch of a cell is turned OFF. Thisoption is effective, for example, when the calibration continues to beexecuted until the switch of the cell is turned OFF.

(5) A radio link configuring the CBS; for example, at least one of theDL and the UL may be set.

(6) A combination of (1) to (5) above

Setting these parameters can identify configurations of the CBS. Theseconfigurations may be changed. In the following description, theparameter for configuring the CBS may be referred to as “CBS settinginformation”.

The following (1) to (3) will be disclosed as example subjects thatconfigure the CBS.

(1) The RRC

(2) The MAC

(3) The PHY processing unit

The base station first configures the CBS. The CBS may be configured bysetting the aforementioned parameters. Accordingly, the subframe onwhich the CBS is configured is identified. Upon determining to executecalibration, the base station sets the CBS to a calibration-specificsubframe. The base station may set the CBS with the necessary timing ofcalibration as an alternative method. The start timing, the end timing,and the period and the duration required for the calibration may be usedto set the CBS. Furthermore, a radio link that performs calibration maybe used to set the CBS. The base station sets the CBS to acalibration-specific subframe.

The base station maps cal-RSs of a transmission antenna for calibrationto the set calibration-specific subframe, and transmits the cal-RSs onthe subframe. Since the other signals and CHs of the cal-RSs are notmapped to the CBS, the calibration-specific subframe can be configured.Many resources can be used for calibration.

When the CBS has transmission data, the base station stops transmittingdata. The transmission data may be held. The method disclosed in thesecond modification of the fourth embodiment may be applied to thismethod. Furthermore, even with occurrence of a signal and a CH to betransmitted irrespective of the transmission data, transmission of thesesignal and CH may be stopped.

FIG. 31 is a flowchart indicating an example procedure on calibrationprocesses in a communication system according to the third modificationof the fourth embodiment. FIG. 31 illustrates an exampleself-calibration in a base station. Furthermore, FIG. 31 illustratessetting of the CBS with the necessary timing of calibration. Since theflowchart of FIG. 31 includes the same steps as those in the flowchartsof FIGS. 28 and 30 as described above, the same step numbers will beassigned to the same Steps and the common description thereof will beomitted.

The base station that determines to execute calibration in Step ST4101sets a CBS in Step ST4401. Here, the base station sets the CBS with thenecessary timing of calibration and according to a radio link thatperforms calibration. After completion of the process in Step ST4401,the processes proceed to Step ST4402.

In Step ST4402, the base station determines whether the timing of theCBS has come. If the base station determines that the timing of the CBShas come, the processes proceed to Step ST4302. If the base stationdetermines that the timing of the CBS has not come, the process in StepST4402 will be repeated until the next timing of the CBS.

In Step ST4302, the base station determines the presence or absence oftransmission data. If the base station determines the presence oftransmission data, the processes proceed to Step ST4303. If the basestation determines the absence of transmission data, the processesproceed to Step ST4403.

In Step ST4303, the base station stops transmitting data with thecalibration timing, and stores the transmission data. After completionof the process in Step ST4303, the processes proceed to Step ST4403.

The base station that stores the transmission data in Step ST4303 mapscal-RSs to the CBS with the necessary timing of calibration, andtransmits the cal-RSs on the CBS in Step ST4403. The base station mayset the CBS with the necessary timing of calibration to acalibration-specific subframe. The base station maps cal-RSs of atransmission antenna for calibration to the set calibration-specificsubframe, and transmits the cal-RSs on the subframe. After completion ofthe process in Step ST4403, the processes proceed to Step ST4105.

After the processes in Steps ST4105 and ST4106, if it is determined inStep ST4107 that calibration on all the antenna elements is completed,the processes proceed to Step ST4304. If it is determined that thecalibration on the entire antenna has not been completed, the processesreturn to Step ST4302 to perform the aforementioned processes on anantenna element that has not been calibrated.

In Step ST4304, the base station resumes transmission of data includingthe stored data, with the timing capable of transmission of data on asubframe that is not a CBS. When the CBS end timing is set, configuringthe CBS ends according to the setting. The entire procedure ends afterthe process in Step ST4304.

Configuring the CBS in advance using the method disclosed in the thirdmodification can facilitate setting of a calibration-specific subframe.Furthermore, setting the CBS with the necessary timing of calibrationenables execution of calibration with the necessary timing.

Accordingly, even when the base station has many UEs being servedthereby or even when a huge volume of data is communicated, it ispossible to prevent degradation in the performance caused by delay inthe calibration. Thus, the performance of the MIMO and the beamformingusing the multi-element antenna can be further improved.

The method according to the first modification of the fourth embodimentmay be applied to a case where there are a signal and a CH to betransmitted irrespective of transmission data with the necessary timingof calibration. Even in the presence of the signal and the CH to betransmitted irrespective of transmission data, a calibration-specificsubframe can be set with the necessary timing of calibration, andcalibration can be performed on the subframe.

Although the third modification discloses configuring the CBS and usingthe CBS for calibration, the CBS may be used for other applicationswithout being limited to the calibration. For example, a subframe thattransmits nothing may be provided to suppress interference betweencells.

Although the fourth embodiment to the third modification thereofdescribe the calibration to be performed by the base station, themethods disclosed in the fourth embodiment to the third modificationthereof are applicable to the calibration to be performed by UEs. Withapplication of the methods disclosed in the fourth embodiment to thethird modification thereof to the calibration to be performed by UEs,the UEs can perform the calibration during their operations.

The methods disclosed in the fourth embodiment to the third modificationthereof are applicable not only to the OFDM as an access scheme but alsoto the other access schemes. With application of the methods disclosedin the fourth embodiment to the third modification thereof to the otheraccess schemes, a system using the other access schemes can perform thecalibration during operation.

Fifth Embodiment

The third and fourth embodiments disclose providing a subframe forcalibration or a calibration-specific subframe. Furthermore, the thirdand fourth embodiments disclose that the base station does not transmitthe other CHs or RSs on the subframe.

Normally, the base station transmits an RS for demodulation and acontrol CH on every DL subframe. The base station transmits, forexample, a CRS and a PDCCH in the LTE. The RS for demodulation is asignal for synchronization and demodulation by a UE. The control CHincludes information required for the UE to receive data.

In the presence of a subframe without an RS for demodulation and acontrol CH, the UE cannot normally receive data on the subframe. Thus,when the UE does not recognize the timing of a subframe for calibration,the UE recognizes the presence of an RS for demodulation and a controlCH on the subframe, and receives the subframe.

Here, the UE has a problem with a possible malfunction because itwrongly receives the subframe based on the assumption of the presence oftransmission data, despite no actual transmission of the data on thesubframe. The fifth embodiment will disclose a method for solving such aproblem.

The base station notifies the UE of information on signals forcalibration. The base station may notify the UE of information on acalibration-specific subframe. The UE does not need to receive data withthe transmission timing of the calibration-specific subframe, using theobtained information on the calibration-specific subframe.

Examples of the information on the calibration-specific subframe includeinformation on the timing to transmit the calibration-specific subframe.The example information is an indication indicating a subframe on whichthe calibration-specific subframe is transmitted.

The indication may be, for example, an indication of a subframe numberor the next subframe. The indication of subframes after the n-thsubframe may be “n”. The indication may indicate whether the subframesare consecutive. Furthermore, the indication may indicate the number ofconsecutive subframes. The indication may be information obtained bycombining these.

Such information is more effective when the immediacy of notifying theUE is required. Such information is effective, for example, when asubframe having no transmission data is detected and the detectedsubframe is set to a calibration-specific subframe, as a method forimmediately notifying the UE.

Examples of the other information on the calibration-specific subframeinclude the CBS setting information disclosed in the third modificationof the fourth embodiment. These parameters are more effective when theimmediacy of notifying the UE is not required. These parameters are moreeffective, for example, when the necessary timing of calibration can berecognized in advance or when the CBS is configured.

Examples of the other information on the calibration-specific subframeinclude time stamps. The system frame number (SFN) has the upper limitvalue. The time stamps are effective when calibration-specific subframesare set at intervals that exceed the upper limit value. The time stampsmay be managed by operation administration and maintenance (OAM) orobtained using the Global Positioning System (GPS).

A method for notifying information on a calibration-specific subframefrom a base station to a UE will be disclosed. The base station notifiesthe UE of the information from a cell to be calibrated. The following(1) to (3) will be disclosed as specific examples of the notificationmethod.

(1) The information is notified by the RRC signaling. The informationmay be broadcast to the UEs being served, or notified individually tothe UEs being served. When the information is broadcast using broadcastinformation, many UEs can be simultaneously notified. When theinformation is notified individually to the UEs, it can be reliablynotified via a retransmission function. This method is highly compatiblewith a case where, for example, each of the subject that detects asubframe having no data to be transmitted or scheduled and the subjectthat sets a subframe to a calibration-specific subframe as disclosed inthe fourth embodiment, and the subject that configures the CBS asdisclosed in the third modification of the fourth embodiment is the RRC.Furthermore, this option is more effective when information on thecalibration-specific subframe does not require the immediacy ofnotifying the UEs.

(2) The information is notified by the MAC signaling. The information isnotified individually to the UEs being served. This method is highlycompatible with a case where, for example, each of the subject thatdetects a subframe having no data to be transmitted or scheduled and thesubject that sets a subframe to a calibration-specific subframe asdisclosed in the fourth embodiment, and the subject that configures theCBS as disclosed in the third modification of the fourth embodiment isthe MAC or the scheduler. Furthermore, this option is more effectivewhen information on the timing to transmit a calibration-specificsubframe requires the immediacy of notifying the UEs.

(3) The information is notified by a physical control channel. Theinformation is notified individually to the UEs being served. Thismethod is highly compatible with a case where, for example, each of thesubject that detects a subframe having no data to be transmitted orscheduled and the subject that sets a subframe to a calibration-specificsubframe as disclosed in the fourth embodiment, and the subject thatconfigures the CBS as disclosed in the third modification of the fourthembodiment is the PHY processing unit. Furthermore, this option is moreeffective when information on the timing to transmit acalibration-specific subframe requires the immediacy of notifying theUEs.

FIG. 32 illustrates an example sequence on calibration in acommunication system according to the fifth embodiment. FIG. 32illustrates an example method for detecting a subframe having no data tobe transmitted or scheduled and setting the subframe to acalibration-specific subframe as disclosed in the fourth embodiment andthe first modification of the fourth embodiment.

In Step ST5101, the base station and a UE perform normal communication.The base station that executes calibration detects anon-transmission-data subframe that is a subframe having no transmissiondata in Step ST5102.

In Step ST5103, the base station sets the detected subframe to acalibration-specific subframe.

In Step ST5104, the base station notifies the UE of information on theset calibration-specific subframe (hereinafter may be referred to as“calibration-specific subframe information”).

In Step ST5105, the base station maps cal-RSs of a transmission antennafor calibration to the calibration-specific subframe during thesubframe, and transmits the cal-RSs on the subframe.

In Step ST5106, the base station performs a normal operation aftertransmitting the cal-RSs on the calibration-specific subframe.

The UE obtains the calibration-specific subframe information in StepST5104. In Step ST5107, the UE stops reception using the obtainedcalibration-specific subframe information, during thecalibration-specific subframe.

In Step ST5108, the UE resumes the reception after thecalibration-specific subframe.

In Step ST5109, the base station and the UE perform normal communicationafter the calibration-specific subframe.

The sequence illustrated in FIG. 32 is more effective when the immediacyof notifying the UE is required. For example, the base station detectsthe non-transmission-data subframe with a scheduler in Step ST5102 andsets the detected subframe to a calibration-specific subframe in StepST5103.

The scheduler notifies the PHY processing unit of information on the setcalibration-specific subframe. The PHY processing unit includes thecalibration-specific subframe information in the physical controlchannel as control information, and notifies the UE of the informationin Step ST5104. Since the scheduler recognizes the amount of data to betransmitted on the next subframe, the PHY processing unit can includeinformation on the calibration-specific subframe detected and set by thescheduler in the physical control channel of a subframe preceding therecognized subframe as control information, and notify the UE of theinformation.

Accordingly, the UE can prevent occurrence of a malfunction caused byreceiving a calibration-specific subframe despite no transmission of anRS for demodulation and a control CH on the subframe, and wronglyreceiving the subframe based on the assumption of the presence oftransmission data despite no actual transmission of the data. Thus, thebase station can calibrate the multi-element antenna with the necessarytiming, without causing the UE to malfunction.

FIG. 33 illustrates another example sequence on calibration in thecommunication system according to the fifth embodiment. FIG. 33illustrates an example method for configuring the CBS that is disclosedin the third modification of the fourth embodiment.

In Step ST5201, the base station and the UE perform normalcommunication. The base station that executes calibration sets the CBSwith the calibration timing in Step ST5202.

In Step ST5203, the base station notifies the UE of information on theset CBS (hereinafter may be referred to as “CBS information”).

The UE that has received the CBS information in Step ST5203 notifies thebase station of a CBS-information notice response in Step ST5204. TheCBS-information notice response in Step ST5204 may be omitted.

The base station that has received the CBS-information notice responsein Step ST5204 transmits cal-RSs on the CBS in Step ST5205.Specifically, the base station maps cal-RSs of a transmission antennafor calibration to the CBS, and transmits the cal-RSs on the CBS.

In Step ST5206, the base station obeys the CBS setting and performs anormal operation after the CBS.

The UE that has notified the base station of the CBS-information noticeresponse in Step ST5204 stops reception on the CBS in Step ST5207.Specifically, the UE stops reception during the CBS, using the obtainedCBS information.

In Step ST5208, the UE resumes the reception after the CBS. In StepST5209, the base station and the UE perform normal communication afterthe CBS.

The sequence illustrated in FIG. 33 is more effective when the immediacyof notifying the UE is not required. In Step ST5202, for example, thebase station causes the RRC to set the CBS. In Step ST5203, the RRCnotifies the UE of the CBS information included in the RRC signaling.

The UE that has received the RRC signaling may perform reception-stopcontrol on the CBS through the RRC, using the obtained CBS information.The RRC in the UE may notify the MAC or the PHY processing unit of thetiming of the CBS to stop receiving data on the subframe. Accordingly,the control by the RRC becomes possible.

For example, when information is sent individually to the UEs beingserved, each of the UEs may notify the base station of theCBS-information notice response, whereas when information is broadcastto the UEs being served, each of the UEs may not notify the base stationof the CBS-information notice response. Accordingly, the UEs can stopreception during the CBS.

Accordingly, the UE can prevent occurrence of a malfunction caused byreceiving the CBS despite no transmission of an RS for demodulation anda control CH on the subframe, and wrongly receiving the subframe basedon the assumption of the presence of transmission data despite no actualtransmission of the data. Thus, the base station can calibrate themulti-element antenna with the necessary timing, without causing the UEto malfunction.

The UE may communicate with another base station (cell) during acalibration-specific subframe. Alternatively, the UE may measure theother base station (cell). The operations of the UE during thecalibration-specific subframe may be predetermined as a system.Alternatively, the base station may determine the operations of the UEduring the calibration-specific subframe and notify the UE of theoperations. This notice may be notified together with information on thecalibration-specific subframe. Accordingly, the UE can use the subframefor other applications.

Furthermore, the base station may notify adjacent base stations ofinformation on a calibration-specific subframe. This notice may benotified by the X2 signaling. Accordingly, the adjacent base stationscan recognize the existence of the calibration-specific subframe, andresources on the time axis or the frequency axis. Furthermore, theadjacent base stations can recognize the absence of transmission dataand the absence of a CH and an RS to be transmitted irrespective of thetransmission data, on the calibration-specific subframe. Thus, forexample, data for the UEs being served can be scheduled using thesubframe, without any concern about interference with adjacent basestations.

Furthermore, the base station may notify a core network side node ofinformation on the calibration-specific subframe. During the calibrationin the base station, the core network side node may notify theinformation on the calibration-specific subframe that is obtained fromthe base station, to a base station that requires some specialoperations. These notices may be notified by the S1 signaling.Accordingly, the same advantages as those when information on thecalibration-specific subframe is notified to the adjacent base stationscan be produced.

The fifth embodiment may be applied not only to the self-calibration butalso to the OTA calibration. In the OTA, for example, the base stationtransmits signals for calibration (cal-RSs), and the UE receives thesignals and derives a calibration value. Thus, transmitting informationon the signals for calibration from the base station enables the UE toreceive the signals and derive the calibration value from the receivedsignals.

For example, in Step ST5107 of FIG. 32, the UE may receive the signalsfor calibration during the calibration-specific subframe, withoutstopping reception. The UE derives the calibration value using thereceived signals for calibration.

Furthermore, similarly in Step ST5207 of FIG. 33, the UE may receive thesignals for calibration on the CBS, without stopping reception on theCBS. The UE derives the calibration value using the received signals forcalibration on the CBS. The UE may notify the base station of thederived calibration value. Accordingly, the base station can perform theOTA calibration of a transmission system antenna.

When a reception system is calibrated, the base station may instruct theUE to transmit signals for calibration. The base station may include theinstruction information in information on the signals for calibration orinformation on a calibration-specific subframe and then may notify theUE of the information. Alternatively, the information may be notified byanother signaling.

The UE that has received the instruction information, for example,transmits the signals for calibration on the subframe derived from theobtained information on the calibration-specific subframe. Upon receiptof the signals for calibration transmitted from the UE on thecalibration-specific subframe, the base station derives the calibrationvalue.

For example, in Step ST5104 of FIG. 32, the base station notifies the UEof information on the calibration-specific subframe which includesinformation instructing transmission of the signals for calibration onthe subframe. The UE that has received the information transmits thesignals for calibration on the calibration-specific subframe in StepST5107.

The base station may receive the signals for calibration on thecalibration-specific subframe in Step ST5105. The base station derivesthe calibration value using the received signals for calibration.

Similarly in Step ST5203 of FIG. 33, the base station notifies the UE ofinformation on the CBS which includes information instructingtransmission of the signals for calibration on the subframe. The UE thathas received the information transmits the signals for calibration onthe calibration-specific subframe in Step ST5207.

The base station may receive the signals for calibration on thecalibration-specific subframe in Step ST5205. The base station derivesthe calibration value using the received signals for calibration.Accordingly, the base station can perform the OTA calibration of atransmission system antenna.

As described above, application of the fifth embodiment to the OTAcalibration enables ease of coordination for calibration between thebase station and the UE, for example, ease of matching the calibrationtiming and the recognition of resources, etc. Thus, the OTA calibrationcan be easily performed during the operations.

As described above, a communication terminal is configured not toreceive a subframe in which cal-RSs are arranged, according to the fifthembodiment. Accordingly, a malfunction of the communication terminal canbe prevented.

First Modification of the Fifth Embodiment

The first modification will disclose another method for solving theproblems in the fifth embodiment. The base station configures the UEsbeing served thereby not to receive a calibration-specific subframe. TheDRX is used in this setting. The base station configures the DRX so thatthe UEs being served thereby do not receive data on acalibration-specific subframe. The base station configures the DRX sothat the UEs being served thereby are in inactivity on thecalibration-specific subframe.

Alternatively, the base station configures the DRX so that the UEs beingserved thereby are not active on the calibration-specific subframe.Furthermore, the base station may not transmit data to the UEs beingserved thereby on the calibration-specific subframe to enableconfiguration of the calibration-specific subframe during inactivity ofthe configured DRX.

The base station notifies the UEs being served thereby of the DRXconfiguration. The notification method defined in the conventionalstandards can be applied to this notification of the DRX configuration.

The UEs being served do not receive data from the own cells duringinactivity of the configured DRX. Thus, the UEs do not receive datawhile the base station is executing calibration.

Accordingly, the UE can prevent occurrence of a malfunction caused byreceiving the calibration-specific subframe despite no transmission ofan RS for demodulation and a control CH on the subframe, and wronglyreceiving the subframe based on the assumption of the presence oftransmission data despite no actual transmission of the data. Thus, thebase station can calibrate the multi-element antenna with the necessarytiming, without causing the UE to malfunction.

Furthermore, the UE does not need any special processes on thecalibration, with the use of the existing function. Furthermore, usingthe existing notification method, there is no need to notify the UE ofparticular signaling for calibration.

Another setting method will be disclosed. A measurement gap is used asthe setting method. The base station configures a measurement gap sothat the UEs being served thereby do not receive data on acalibration-specific subframe. The base station configures a measurementgap to include a calibration-specific subframe, for the UEs being servedthereby.

The base station notifies the UEs being served thereby of themeasurement gap configuration. The notification method defined in theconventional standards can be applied to this notification of themeasurement gap configuration. When the DL is used for calibration, ameasurement gap for the DL may be configured. When the UL is used forcalibration, a measurement gap for the UL may be configured.

The UEs being served do not receive data from the own cells during theconfigured measurement gap. Thus, the UEs do not receive data while thebase station is executing calibration. The UEs can produce the sameadvantages as described above.

Although the DRX is configured only in the DL, the measurement gap canbe set also in the UL. Thus, even when calibration is performed in theUL, using the measurement gap is effective.

The methods disclosed in the fifth embodiment and the first modificationthereof are applicable not only to the OFDM as an access scheme but alsoto the other access schemes.

Sixth Embodiment

The third embodiment discloses arranging RSs for calibration, and otherCHs or other RSs in the same subframe. The sixth embodiment willdisclose the specific examples.

A base station uses a physical downlink shared channel region fortransmitting cal-RSs. The base station maps the cal-RSs to the physicaldownlink shared channel region. A physical downlink shared channel isnot mapped to the symbols to which the cal-RSs are mapped. The ratematching and coding may be performed so that the physical downlinkshared channel is not mapped to the symbols to which the cal-RSs aremapped.

Alternatively, after mapping a physical downlink shared channel to aphysical downlink shared channel region, the base station may replacethe symbols to which cal-RSs are mapped with the cal-RSs. The basestation does not transmit the physical downlink shared channel on thesymbols to which the cal-RSs are mapped.

Accordingly, the RSs for calibration can be orthogonal to the other CHsand the other RSs in a frequency domain and a time domain. Thus, the RSsfor calibration, the other CHs, and the other RSs can be arranged in thesame subframe, and calibration can be performed during communication.

FIG. 34 illustrates an example configuration of a subframe when cal-RSsare mapped to a physical downlink shared channel region. The horizontalaxis represents a time t, and the vertical axis represents a frequency fin FIG. 34. FIG. 34 illustrates an example in the LTE. In FIG. 34, areference “6001” denotes a subframe, and a reference “6002” denotesymbol timing. In one subframe, the first 3 symbols form a PDCCH region6003, and the subsequent 11 symbols form a PDSCH region 6004.

CRSs 6005 are mapped over the PDCCH region 6003 and the PDSCH region6004. A PDCCH and a PCFICH, etc. are mapped to the PDCCH region 6003.PDSCHs are mapped to the PDSCH region 6004.

FIG. 34 illustrates an example of mapping cal-RSs to the PDSCH region6004. Cal-RSs 6006 of a first antenna element #1, cal-RSs 6007 of asecond antenna element #2, cal-RSs 6008 of a third antenna element #3,and cal-RSs 6009 of a fourth antenna element #4 are mapped to the PDSCHregion 6004. PDSCHs 6010 are mapped to the other symbols.

Such mapping of the cal-RSs 6006 to 6009 to the PDSCH region 6004enables mapping of the cal-RSs 6006 to 6009, the PDSCHs 6010, the PDCCH,and the CRSs 6005 within the same subframe. The base station cantransmit the cal-RSs 6006 to 6009, the PDSCHs, the PDCCH, and the CRSs6005 on the same subframe. Thus, calibration is possible during the datacommunication with the UE.

Another method will be disclosed. The base station may not map aphysical downlink shared channel to a slot or a subframe to whichcal-RSs are mapped. The methods disclosed in the fourth embodiment andthe second modification of the fourth embodiment may be applied tohandling of the transmission data on the subframe.

The base station may map cal-RSs to a subframe except for subframes towhich physical downlink shared channels where a paging channel, abroadcast channel, or a random access response is mapped are mapped. Thebase station may not map a physical downlink shared channel over theentire frequency domain with the symbol timing to map the cal-RSs. Thebase station may map the cal-RSs with the symbol timing different fromthat of a synchronization signal, a physical broadcast channel, or theother RSs.

FIG. 35 illustrates another example configuration of a subframe whencal-RSs are mapped to a physical downlink shared channel region. Thehorizontal axis represents a time t, and the vertical axis represents afrequency f in FIG. 35. FIG. 35 illustrates an example in the LTE. InFIG. 35, a reference “6101” denotes a subframe, and a reference “6102”denotes symbol timing. In one subframe, the first 3 symbols form a PDCCHregion 6103, and the subsequent 11 symbols form a PDSCH region 6104.

CRSs 6105 are mapped over the PDCCH region 6103 and the PDSCH region6104. A PDCCH and a PCFICH, etc. are mapped to the PDCCH region 6103.

FIG. 35 illustrates an example of mapping cal-RSs to the PDSCH region6104 without mapping a PDSCH. A cal-RS 6106 of the first antenna element#1, a cal-RS 6107 of the second antenna element #2, a cal-RS 6108 of thethird antenna element #3, and a cal-RS 6109 of the fourth antennaelement #4 are mapped to the PDSCH region 6104 without mapping anyPDSCH. FIG. 35 illustrates an example in which the base station maps thecal-RSs over the entire frequency domain with the symbol timing to mapthe cal-RSs 6106 to 6109.

Such mapping of the cal-RSs 6106 to 6109 to the PDSCH region 6104enables mapping of the cal-RSs 6106 to 6109, the PDCCH, and the CRSs6105 within the same subframe. The base station can transmit the cal-RSs6106 to 6109, the PDCCH, and the CRSs 6105 on the same subframe. Sincethe control channel and the signals used in demodulation and measurementare transmitted, the base station can execute calibration duringcommunication with the UE.

Furthermore, the base station does not schedule the UE using the PDCCH.Accordingly, the UE does not need to receive the PDSCH, and occurrenceof a malfunction in the UE can be reduced.

Another example will be disclosed. Instead of the physical downlinkshared channel, a multimedia broadcast multicast service singlefrequency network (MBSFN) region is used. Furthermore, although a PMCHand a PDSCH are mapped to the MBSFN region, both the PMCH and the PDSCHmay replace the PDSCHs described above.

Accordingly, the RSs for calibration can be orthogonal to the other CHsand the other RSs in a frequency domain and a time domain. Thus, the RSsfor calibration, the other CHs, and the other RSs can be arranged in thesame subframe, and calibration can be performed during communication.

FIG. 36 illustrates an example configuration of a subframe when cal-RSsare mapped to an MBSFN region. The horizontal axis represents a time t,and the vertical axis represents a frequency fin FIG. 36. FIG. 36illustrates an example in the LTE. In FIG. 36, a reference “6201”denotes the MBSFN subframe, and a reference “6202” denotes symboltiming. In one subframe, the first 2 symbols form a non-MBSFN region6203, and the subsequent 12 symbols form an MBSFN region 6204.

The CRSs 6105 are mapped to the non-MBSFN region 6203. A PDCCH and aPCFICH, etc. are mapped to the non-MBSFN region 6203. A PMCH and a PDSCHcan be mapped to the MBSFN region 6204.

FIG. 36 illustrates an example of mapping cal-RSs to the MBSFN region6204 without mapping any PMCH. The cal-RS 6106 of the first antennaelement #1, the cal-RS 6107 of the second antenna element #2, the cal-RS6108 of the third antenna element #3, and the cal-RS 6109 of the fourthantenna element #4 are mapped to the MBSFN region 6204 without mappingany PMCH and any PDSCH. FIG. 36 illustrates an example in which the basestation maps the cal-RSs over the entire frequency domain with thesymbol timing to map the cal-RSs 6106 to 6109.

Such mapping of the cal-RSs 6106 to 6109 to the MBSFN region 6204enables mapping of the cal-RSs 6106 to 6109, the PDCCH, and the CRSs6105 within the same subframe. The base station can transmit the cal-RSs6106 to 6109, the PDCCH, and the CRSs 6105 on the same subframe. Sincethe control channel and the signals used in demodulation and measurementare transmitted, the base station can execute calibration duringcommunication with the UE.

Furthermore, the base station does not schedule the UE using the PDCCH.Accordingly, the UE does not need to receive the PDSCH, and occurrenceof a malfunction in the UE can be reduced.

When the PMCH is not transmitted in the MBSFN region 6204, the basestation does not transmit an RS for MBSFN. Thus, when neither the PMCHnor the PDSCH is mapped to the MBSFN region 6204, nothing is mapped tothe MBSFN region 6204. Accordingly, resources can be allocated tocalibration more than those when the PDSCH region is used.

Furthermore, the MBSFN subframe is not configured in a subframe to whicha synchronization signal, a physical broadcast channel, or a pagingchannel is mapped. Thus, configuring an MBSFN subframe and mappingcal-RSs to the MBSFN subframe enables the base station to eliminate aprocess of mapping cal-RSs to a symbol or a subframe except for symbolsto which the synchronization signal and the physical broadcast channelare mapped and subframes to which a paging channel is mapped, if such aprocess exists. Accordingly, the processes performed by the base stationcan be simplified.

Another example will be disclosed. An almost blank subframe (ABS) isused. The ABS is a subframe to which the other CHs and RSs than the CRSsare not mapped. Mapping the RSs for calibration to a resource to whichthe CRSs of the ABS are not mapped enables orthogonalization of the RSsfor calibration with the other RSs (CRSs) in a frequency domain and atime domain. Thus, the RSs for calibration and the other RSs can bearranged in the same subframe, and calibration can be performed duringcommunication.

FIG. 37 illustrates an example configuration of a subframe when cal-RSsare mapped to an ABS region. The horizontal axis represents a time t,and the vertical axis represents a frequency fin FIG. 37. FIG. 37illustrates an example in the LTE. In FIG. 37, a reference “6301”denotes the ABS region, and a reference “6302” denotes symbol timing.

The CRSs 6105 are mapped to the ABS region 6301. The cal-RS 6106 of thefirst antenna element #1, the cal-RS 6107 of the second antenna element#2, the cal-RS 6108 of the third antenna element #3, and the cal-RS 6109of the fourth antenna element #4 are mapped to a resource where the CRSs6105 are not mapped in the ABS region 6301. FIG. 37 illustrates anexample in which the base station maps the cal-RSs over the entirefrequency domain with the symbol timing to map the cal-RSs 6106 to 6109.

Such mapping of the cal-RSs 6106 to 6109 to the ABS region 6301 enablesmapping of the cal-RSs 6106 to 6109 and the CRSs 6105 within the samesubframe. The base station can transmit the cal-RSs 6106 to 6109 and theCRSs 6105 on the same subframe. Since the signals used in demodulationand measurement are transmitted, the base station can executecalibration during communication with the UE.

Furthermore, any PDCCH is not transmitted in the ABS region 6301. If theABS has been configured, the UE that is notified of the configuration ofthe ABS from the base station does not have to receive the ABS. The UEdoes not need to receive the ABS, and occurrence of a malfunction in theUE can be reduced.

Furthermore, neither a PDCCH nor a PCFICH is transmitted in the ABSregion 6301. Since the PDCCH region can also be used as a resource forcalibration, resources can be allocated to calibration more than thosewhen the PDSCH region is used.

Furthermore, the ABS is not configured in a subframe to which asynchronization signal, a physical broadcast channel, or a pagingchannel is mapped. Thus, configuring an ABS and mapping cal-RSs to theABS enables the base station to eliminate a process of mapping cal-RSsto a symbol or a subframe except for symbols to which thesynchronization signal and the physical broadcast channel are mapped andsubframes to which a paging channel is mapped, if such a process exists.Accordingly, the processes performed by the base station can besimplified.

Furthermore, the UE that performs calibration may not be notified of,particularly, information on cal-RSs from the base station, with themethod disclosed in the fifth embodiment. The UE may follow thescheduling by the PDCCH, the setting of the MBSFN subframe, and thesetting of the ABS as conventionally performed. Thus, the UE neitherneeds to recognize the calibration nor needs any special processes onthe calibration. Accordingly, the processes performed by the UE can besimplified.

The base station may specify information on the cal-RSs to the UE. Thebase station may notify the UE of the information on the cal-RSs.Examples of the information on the cal-RSs include a radio frame, asubframe, a resource, and a sequence to which the cal-RSs are mapped.Examples of the resource include a resource block, a resource element,and a resource unit, etc.

Examples of the notification method includes notification by the RRCsignaling, the MAC signaling, and the PDCCH. For example, when cal-RSsare mapped to a PDSCH region, the base station notifies the UE ofinformation on the cal-RSs.

Accordingly, the UE can recognize a subframe, a resource, and a sequenceto be calibrated. For example, the UE can determine the absence of aPDSCH in a resource to which the cal-RSs are mapped, among the receivedsubframes.

Thus, the UE can perform a process of, for example, not receiving theresource or discarding a result of demodulation on the resource.Accordingly, the UE can accurately receive the resource of the PDSCH.

The same holds true when the MBSFN subframe is used. The base stationmay notify the UE of information on the MBSFN subframe to which thecal-RSs are mapped. The configuration of the MBSFN subframe may benotified including the information on the MBSFN subframe to which thecal-RSs are mapped. For example, the UE can determine the absence of aPMCH or a PDSCH in a resource to which the cal-RSs are mapped, among theMBSFN subframes.

Thus, the UE can perform a process of, for example, not receiving theresource or discarding a result of demodulation on the resource.Accordingly, the UE can accurately receive the resource of the PMCH orthe PDSCH.

The same holds true when the ABS is used. The base station may notifythe UE of information on the ABS to which the cal-RSs are mapped. Theconfiguration of the ABS may be notified including the information onthe ABS to which the cal-RSs are mapped. Accordingly, the UE canrecognize a subframe to be calibrated.

Thus, even if the UE can receive RSs for calibration, it can recognizethat the signals are for calibration. Thus, the UE can perform a processof, for example, not receiving the resource or discarding a result ofdemodulation on the resource. Accordingly, it is possible to prevent theUE from wrongly receiving the ABS.

Furthermore, the base station may notify the adjacent base stations ofinformation on the cal-RSs, information on the MBSFN subframe to whichthe cal-RSs are mapped, and information on the ABS to which the cal-RSsare mapped. This notice may be notified by the X2 signaling.

Normally, the adjacent base stations do not recognize transmission ofthe cal-RSs on a normal subframe, the MBSFN subframe, and the ABS. Inthe case where the cal-RSs have to be transmitted with high power forcalibration, the signals may interfere the adjacent base stations.

Thus, notifying, from the base station, the adjacent base stations ofthe information on the cal-RSs, the information on the MBSFN subframe towhich the cal-RSs are mapped, and the information on the ABS to whichthe cal-RSs are mapped enables the adjacent base stations to recognizethe existence of the cal-RSs and the resources on the time axis or thefrequency axis. Consequently, for example, the adjacent base stationscan avoid data scheduling of the UEs being served thereby, based on theassumption of the interference from the base station.

Furthermore, the base station may notify the core network side node ofinformation on the cal-RSs, information on the MBSFN subframe to whichthe cal-RSs are mapped, and information on the ABS to which the cal-RSsare mapped.

During the calibration in the base station, the core network side nodemay notify the information on the cal-RSs, the information on the MBSFNsubframe to which the cal-RSs are mapped, and the information on the ABSto which the cal-RSs are mapped all of which are obtained from the basestation, to a base station that requires some special operations.

These notices may be notified by the S1 signaling. Accordingly, the sameadvantages as those in the previous embodiments can be produced evenwhen the base station notifies the core network side node of theinformation on the cal-RSs, the information on the MBSFN subframe towhich the cal-RSs are mapped, and the information on the ABS to whichthe cal-RSs are mapped.

Seventh Embodiment

The second, third, and sixth embodiments disclose calibrating everyantenna element using RSs for calibration. According to theseembodiments, as the number of the antenna elements increases, thecal-RSs also increases. Thus, when all the antenna elements arecalibrated, the time to adjust the phase and the amplitude of each ofthe antenna elements increases. Furthermore, as the cal-RSs increases,the overhead increases. Accordingly, a physical region for downlinkavailable for actual communication decreases, and thus a problem withincapability to guarantee the communication performance that isoriginally expected occurs. The seventh embodiment will disclose amethod for solving such problems.

The antenna elements included in a multi-element antenna of the basestation are grouped. Examples of the method for grouping the antennaelements include a grouping method relying on adjustment resultsobtained through calibration executed to form beams by the multi-elementantenna before shipment, before setting, and during operations, and agrouping method based on a structure of the multi-element antenna.

When the antenna elements are grouped according to the adjustmentresults obtained through calibration, data of amplitude adjustmentvalues and phase adjustment values obtained as the adjustment resultsare stored as calibration values obtained from the calibration in thepast, and the antenna elements having the adjustment values within apredetermined range are grouped. Examples of the predetermined rangeinclude a range of ±1 bit of adjustment results obtained from a digitalphase shifter used in adjusting the phase. Thus, the antenna elementswhose adjustment results from the digital phase shifter fall within therange of ±1 bit are handled as the same group.

In addition to this, in a multi-element antenna for transmission,transmission signals output from the respective antenna elements can begrouped according to signal levels received by a reference receptionsystem. Furthermore, in a multi-element antenna for reception, groupingaccording to signal levels obtained by receiving, through the respectiveantenna elements, a transmission signal output from a referencetransmission system is possible.

Here, the reference reception system and the reference transmissionsystem are included in an arbitrary antenna element in the multi-elementantenna. The arbitrary antenna element is, for example, an antennaelement located in the center of all the antenna elements, an antennaelement each located at the four corners of a set of all the antennaelements, one antenna element in horizontal and vertical arrays ofantenna elements, or an antenna element located in the center of antennaelements formed per sub-array antenna.

Examples of the method for grouping the antenna elements based on astructure of the multi-element antenna include grouping every antennaelements at an equal distance from a reference antenna element, groupingevery antenna elements collocated in the horizontal or verticaldirection, grouping antenna elements according to the power distributionin a tapered sub-array antenna, and grouping antenna elements everyvertically polarized waves and every horizontally polarized waves when apolarized wave antenna is configured.

With application of the grouping method according to a distance from areference antenna element, a permissible accuracy can be relaxed inadjustment performed every antenna group. The tapered sub-array antennais configured with weighting of the power distribution within themulti-element antenna, in order to reduce the side lobe level in anantenna radiation pattern. Thus, main antenna elements that determinethe beam shape, are positioned in the center, and have larger output intransmission are grouped, and only these main antenna elements arecalibrated. Accordingly, the time to adjust the phase and the amplitudeof each of the antenna elements can be shortened.

Since in the configuration of the polarized wave antenna, the radiowaves in the vertically polarized waves and in the horizontallypolarized waves are orthogonal to one another in their relationship,signals simultaneously transmitted and received are less subject tomutual interference. Thus, grouping antenna elements for every polarizedwaves enables simultaneous calibration of a vertical antenna and ahorizontal antenna.

A method for calibrating an antenna element group obtained by suchgrouping will be hereinafter described.

When a multi-element antenna for transmission is calibrated, any one ofthe antenna elements in each antenna group transmits cal-RSs, and aresult of the calibration obtained by receiving the signals through areference reception system is reflected on all the antenna elements inthe same group.

When a multi-element antenna for reception is calibrated, any one of theantenna elements in the group receives cal-RSs output from a referencetransmission system. Then, a result of the calibration obtained throughthe reception is reflected on all the antenna elements in the samegroup.

FIG. 38 illustrates an example configuration of a subframe when cal-RSsof each antenna group are mapped to a physical downlink shared channelregion according to the seventh embodiment. The horizontal axisrepresents a time t, and the vertical axis represents a frequency finFIG. 38.

In FIG. 38, a reference “7101” denotes a subframe, a reference “7102”denotes symbol timing, and a reference “7105” denotes a CRS. In onesubframe, the first 3 symbols form a PDCCH region 7103, and thesubsequent 11 symbols form a PDSCH region 7104.

In contrast to the example disclosed in the sixth embodiment of mappingthe cal-RSs to a physical downlink shared channel region in the LTE,FIG. 38 illustrates an example of arranging cal-RSs for each antennagroup. Since the configuration of the physical downlink channel exceptfor the cal-RSs is the same as that in FIG. 35, the description thereofwill be omitted.

FIG. 38 illustrates an example of mapping the cal-RSs for each antennagroup, without mapping a PDSCH. A cal-RS 7106 of a first antenna group#1, a cal-RS 7107 of a second antenna group #2, a cal-RS 7108 of a thirdantenna group #3, and a cal-RS 7109 of a fourth antenna group #4 aremapped to the PDSCH region 7104 without mapping a PDSCH.

FIG. 38 illustrates an example in which the base station maps thecal-RSs over the entire frequency domain with the symbol timing to mapthe cal-RSs 7106 to 7109 for each antenna group.

Since the antenna elements are grouped and the cal-RSs are set for eachantenna group as described above, the number of the cal-RSs can bereduced more than that when the cal-RSs are used for each of the antennaelements. Accordingly, the time to adjust the phase and the amplitude ofeach of the antenna elements can be shortened. Furthermore, reduction inthe number of the cal-RSs can prevent degradation in the communicationperformance caused by overhead.

Furthermore, using both the grouping method relying on adjustmentresults obtained through calibration and the grouping method based onthe structure of the multi-element antenna can, for example, relax theaccuracy in adjusting the phase and the amplitude of each of the antennaelements and simplify such adjustment. Accordingly, the time requiredfor calibration can be shortened.

According to the seventh embodiment, the PHY processing unit that is acalibration unit divides a plurality of antenna elements into groups,and sets the cal-RSs for each of the groups. Accordingly, increase inthe cal-RSs can be suppressed. Thus, increase in the time required forcalibration can be suppressed. Furthermore, it is possible to preventdecrease in the physical region for downlink available for actualcommunication and guarantee the communication performance.

Eighth Embodiment

The eighth embodiment will disclose an example of partially thinning outthe cal-RSs mapped over the entire frequency domain with the symboltiming and arranging the cal-RSs, in each of the antenna elementsincluded in the multi-element antenna according to the second, third,and sixth embodiments.

FIG. 39 illustrates an example configuration of a subframe when cal-RSsare mapped to a part of the frequency axis in a physical downlink sharedchannel region according to the eighth embodiment. The horizontal axisrepresents a time t, and the vertical axis represents a frequency finFIG. 39.

In FIG. 39, a reference “8101” denotes a subframe, a reference “8102”denotes symbol timing, and a reference “8105” denotes a CRS. In onesubframe, the first 3 symbols form a PDCCH region 8103, and thesubsequent 11 symbols form a PDSCH region 8104.

FIG. 39 illustrates an example of thinning out and arranging the cal-RSson the frequency axis, in contrast to the example disclosed in the sixthembodiment of mapping the cal-RSs to a physical downlink shared channelregion in the LTE over the entire frequency domain. Since theconfiguration of the physical downlink channel except for the cal-RSs isthe same as that in FIG. 35, the description thereof will be omitted.

FIG. 39 illustrates an example of periodically thinning out the cal-RSsof the antenna elements on the frequency axis and mapping the cal-RSs tothe PDSCH region 8104 without mapping a PDSCH. Cal-RSs 8106 of the firstantenna element #1, cal-RSs 8107 of the second antenna element #2,cal-RSs 8108 of the third antenna element #3, and cal-RSs 8109 of thefourth antenna element #4 are periodically thinned out and mapped to thePDSCH region 8104 with the symbol timing on the frequency axis, withoutmapping a PDSCH.

The cal-RSs for each antenna element may be arranged at fixedfrequencies according to the frequency characteristics of each of theantenna elements, instead of the method for periodically thinning outand arranging the cal-RSs on the frequency axis.

Accordingly, thinning out the cal-RSs of each of the antenna elements onthe frequency axis reduces the number of the cal-RSs arranged in aphysical downlink shared channel region. Thus, another channel can bearranged, and degradation in the communication performance caused byoverhead can be prevented.

FIG. 40 illustrates another example configuration of a subframe whencal-RSs are mapped to a part of the frequency axis in a physicaldownlink shared channel region according to the eighth embodiment. FIG.40 illustrates arranging cal-RSs of a plurality of antenna elementswithin the same symbol timing when the cal-RSs of each of the antennaelements are periodically thinned out and arranged on the frequencyaxis.

The horizontal axis represents a time t, and the vertical axisrepresents a frequency fin FIG. 40. In FIG. 40, a reference “8201”denotes a subframe, a reference “8202” denotes symbol timing, and areference “8205” denotes a CRS. In one subframe, the first 3 symbolsform a PDCCH region 8203, and the subsequent 11 symbols form a PDSCHregion 8204.

In FIG. 40, cal-RSs 8206 of the first antenna element #1, cal-RSs 8207of the second antenna element #2, and cal-RSs 8208 of the third antennaelement #3 are periodically arranged within the same symbol timing inthe PDSCH region 8204 on the frequency axis, without mapping a PDSCH tothe PDSCH region 8204.

Accordingly, arranging the cal-RSs of a plurality of antenna elementswithin the same symbol timing can process the cal-RSs per symbol timing,and reserve a substantial channel region. Accordingly, the processingload can be reduced, and the communication performance can be improved.

Furthermore, with the combination of the seventh and eighth embodiments,it is possible to group antenna elements having the same frequencycharacteristics, and execute calibration using cal-RSs for each of theantenna element groups each of which is obtained by thinning out thecal-RSs of any one of the antenna elements and arranging the the cal-RSson the frequency axis.

FIG. 41 illustrates an example configuration of a subframe when cal-RSsfor each antenna group are mapped to a part of the frequency axis in aphysical downlink shared channel region according to the eighthembodiment. The horizontal axis represents a time t, and the verticalaxis represents a frequency fin FIG. 41. In FIG. 41, a reference “8301”denotes a subframe, a reference “8302” denotes symbol timing, and areference “8305” denotes a CRS. In one subframe, the first 3 symbolsform a PDCCH region 8303, and the subsequent 11 symbols form a PDSCHregion 8304.

FIG. 41 illustrates an example of arranging the cal-RSs thinned out onthe frequency axis for each antenna group, in a physical downlink sharedchannel region in the LTE.

In FIG. 41, cal-RSs 8306 of the first antenna group #1, cal-RSs 8307 ofthe second antenna group #2, cal-RSs 8308 of the third antenna group #3,and cal-RSs 8309 of the fourth antenna group #4 are thinned out andarranged in the PDSCH region 8304 on the frequency axis, without mappinga PDSCH.

With such a configuration, the number of the cal-RSs arranged in aphysical downlink shared channel region is reduced. Accordingly, thetime required for calibration can be shortened, and degradation in thecommunication performance caused by overhead can be prevented.

Furthermore, making null the regions other than the cal-RSs thinned outand arranged on the frequency axis can increase the transmission powerand improve the SNR. Accordingly, the communication performance can beimproved.

As described above, the PHY processing unit that is a calibration unitarranges the cal-RSs in a part of the entire frequency domain of asubframe, according to the eighth embodiment. In other words, the PHYprocessing unit partially thins out and arranges cal-RSs mapped over theentire frequency domain. Accordingly, the time required for calibrationcan be reduced. Furthermore, degradation in the communicationperformance caused by overhead can be prevented.

Although the previous embodiments describe a case where the unit ofresource to be set for calibration is a subframe, not limited to thesubframe but the unit of transmission time in a system may be the unitof resource. The unit of resource may be, for example, a TTI, a slot, ora symbol. Furthermore, the unit of resource may be an integer multipleof the unit of transmission time.

Although the previous embodiments describe a case where the unit ofresource for cal-RSs is a symbol, not limited to the symbol but thebasic time unit in a system may be the unit of resource. Furthermore,the unit of resource may be an integer multiple of the basic time unit.For example, the unit of resource may be the timing of fast Fouriertransform (FFT) in the OFDM. For example, the unit of resource may bethe basic time unit (Ts) in the LTE.

Accordingly, flexible calibration can be performed on the time axis.Thus, execution of the calibration during operation is facilitated, andaccuracy in the calibration can be improved. Thus, the performance ofthe MIMO and the beamforming using the multi-element antenna can befurther improved.

The embodiments and the modifications thereof are merely illustrationsof the present invention and can be freely combined within the scope ofthe invention. Also, any constituent elements of the embodiments and themodifications thereof can be appropriately modified or omitted. Suchfree combination of the embodiments and the modifications thereof andappropriate modification or omission of any constituent elements of theembodiments and the modifications thereof enable appropriate calibrationaccording to an operational environment, and further improvement in theperformance of the MIMO and the beamforming using the multi-elementantenna.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It istherefore understood that numerous modifications and variations can bedevised without departing from the scope of the invention.

DESCRIPTION OF REFERENCES

801, 901, 901A PHY, 802, 909 first antenna element, 803, 922 secondantenna element, 804 third antenna element, 805, 935 n-th antennaelement, 806, 9411, 9412 control unit, 902, 902A first encoder unit, 903first transmission data generating unit, 904 first calibration RSmapping unit, 905 first transmission power setting unit, 9061 firsttransmission correction processing unit, 9062 first transmission phaserotation unit, 907 first modulating unit, 908 first switching unit, 910first demodulating unit, 911, 911A first decoder unit, 9121 firstreception correction processing unit, 9122 first reception phaserotation unit, 913 first calibration RS extracting unit, 914 firstresponse characteristics calculating unit, 915, 915A second encoderunit, 916 second transmission data generating unit, 917 secondcalibration RS mapping unit, 918 second transmission power setting unit,9191 second transmission correction processing unit, 9192 secondtransmission phase rotation unit, 920 second modulating unit, 921 secondswitching unit, 923 second demodulating unit, 924, 924A second decoderunit, 9251 second reception correction processing unit, 9252 secondreception phase rotation unit, 926 second calibration RS extractingunit, 927 second response characteristics calculating unit, 928, 928An-th encoder unit, 929 n-th transmission data generating unit, 930 n-thcalibration RS mapping unit, 931 n-th transmission power setting unit,9321 n-th transmission correction processing unit, 9322 n-thtransmission phase rotation unit, 933 n-th modulating unit, 934 n-thswitching unit, 936 n-th demodulating unit, 937, 937A n-th decoder unit,9381 n-th reception correction processing unit, 9382 n-th receptionphase rotation unit, 939 n-th calibration RS extracting unit, 940 n-thresponse characteristics calculating unit.

1. A communication system comprising a base station device and acommunication terminal device between which a signal is transmitted andreceived through a multi-element antenna including a plurality ofantenna elements, wherein at least one of said base station device andsaid communication terminal device includes a calibration unit thatperforms calibration of phases and amplitudes of beams formed by saidantenna elements when said signal is transmitted and received, and thecalibration unit is configured to arrange a plurality of calibrationreference signals to be transmitted from the plurality of antennaelements, in positions of a subframe in which neither reference signalsnor physical channels are arranged, and transmit the plurality ofcalibration reference signals.
 2. The communication system according toclaim 1, wherein the reference signals or the physical channels arearranged in OFDM symbols that are not adjacent to each other, and theplurality of calibration reference signals are arranged in OFDM symbolsbetween the reference signals or between the physical channels.
 3. Thecommunication system according to claim 1, wherein the reference signalsor the physical channels are arranged in OFDM symbols that are notadjacent to each other, and when OFDM symbols in which the plurality ofcalibration reference signals should be arranged overlap OFDM symbols inwhich the reference signals or the physical channels should be arranged,the plurality of calibration reference signals are preferentiallyarranged in the OFDM symbols.
 4. The communication system according toclaim 1, wherein the reference signals or the physical channels arearranged in OFDM symbols that are not adjacent to each other, and whenOFDM symbols in which the plurality of calibration reference signalsshould be arranged overlap OFDM symbols in which the reference signalsor the physical channels should be arranged, the reference signals orthe physical channels are preferentially arranged in the OFDM symbols.5. A base station device that transmits and receives a signal through amulti-element antenna including a plurality of antenna elements, thebase station device comprising a calibrating unit configured to performcalibration of phases and amplitudes of beams formed by the antennaelements when the signal is transmitted and received, wherein thecalibration unit is configured to arrange a plurality of calibrationreference signals to be transmitted from the plurality of antennaelements, in positions of a subframe in which neither reference signalsnor physical channels are arranged, and transmit the plurality ofcalibration reference signals.
 6. A communication terminal device thattransmits and receives a signal through a multi-element antennaincluding a plurality of antenna elements, the communication terminaldevice comprising a calibrating unit configured to perform calibrationof phases and amplitudes of beams formed by the antenna elements whenthe signal is transmitted and received, wherein the calibration unit isconfigured to arrange a plurality of calibration reference signals to betransmitted from the plurality of antenna elements, in positions of asubframe in which neither reference signals nor physical channels arearranged, and transmit the plurality of calibration reference signals.